BP Midstream Partners (BPMP) 10-K 25 Feb 21 2020 FY Annual report Financial data

Cover

Cover - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Feb. 24, 2021	Jun. 30, 2020
Entity Information [Line Items]
Document Type		10-K
Document Annual Report		true
Document Period End Date		Dec. 31, 2020
Document Transition Report		false
Entity File Number		001-38260
Entity Registrant Name		BP Midstream Partners LP
Entity Incorporation, State or Country Code		DE
Entity Tax Identification Number		82-1646447
Entity Address, Address Line One		501 Westlake Park Boulevard
Entity Address, City or Town		Houston
Entity Address, State or Province		TX
Entity Address, Postal Zip Code		77079
City Area Code		281
Local Phone Number		366-2000
Title of 12(b) Security		Common Units, Representing Limited Partner Interests
Trading Symbol		BPMP
Security Exchange Name		NYSE
Entity Well Known Seasoned Issuer		No
Entity Voluntary Filers		No
Entity Current Reporting Status		Yes
Entity Interactive Data Current		Yes
Entity Filer Category		Accelerated Filer
Entity Small Business		false
Entity Emerging Growth Company		false
ICFR Auditor Attestation Flag		true
Entity Shell Company		false
Entity Public Float				$ 548
Documents Incorporated by Reference	None
Amendment Flag		false
Document Fiscal Year Focus		2020
Entity Central Index Key		0001708301
Current Fiscal Year End Date		--12-31
Document Fiscal Period Focus		FY
Common Units
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding			104,778,502

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets
Cash and cash equivalents	$ 126,900	$ 98,800
Accounts receivable – third parties	200	600
Accounts receivable – related parties	11,000	11,300
Prepaid expenses	6,600	5,100
Other current assets	2,900	5,000
Total current assets	147,600	120,800
Equity method investments (Note 6)	519,900	534,400
Property, plant and equipment, net (Note 7)	67,900	62,700
Other assets	3,500	4,200
Total assets	738,900	722,100
Current liabilities
Accounts payable – third parties	1,900	600
Accounts payable – related parties	1,900	1,700
Deferred revenues and credits – related parties	1,800	1,500
Other current liabilities (Note 8)	7,800	6,600
Total current liabilities	13,400	10,400
Long-term debt – related parties (Note 9)	468,000	468,000
Other Liabilities, Noncurrent	3,500	3,500
Total liabilities	484,900	481,900
Commitments and contingencies (Note 13)
EQUITY
General Partners' Capital Account	1,200	1,200
Total partner's capital	121,500	103,300
Non-controlling interests	132,500	136,900
Total equity	254,000	240,200
Total liabilities and equity	738,900	722,100
Common Units | General Public
EQUITY
Common and subordinated unitholders	860,100	851,600
Common Units | BP Holdco
EQUITY
Common and subordinated unitholders	(59,600)	(60,300)
Subordinated Units | BP Holdco
EQUITY
Common and subordinated unitholders	$ (680,200)	$ (689,200)

CONSOLIDATED BALANCE SHEEETS (P

CONSOLIDATED BALANCE SHEEETS (Parenthetical) - shares	Dec. 31, 2020	Dec. 31, 2019
Common Units | General Public
Common units outstanding (in shares)	47,821,790	47,806,563
Units issued (in shares)	47,821,790	47,806,563
Common Units | BP Holdco
Common units outstanding (in shares)	4,581,177	4,581,177
Units issued (in shares)	4,581,177	4,581,177
Subordinated Units | BP Holdco
Common units outstanding (in shares)	52,375,535	52,375,535
Units issued (in shares)	52,375,535	52,375,535

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Millions	2 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue
Third parties		$ 2,900,000	$ 3,000,000	$ 2,800,000
Related parties		126,000,000	125,500,000	113,600,000
Total revenue		128,900,000	128,500,000	116,400,000
Costs and expenses
Operating expenses – third parties		14,300,000	14,200,000	11,500,000
Operating expenses – related parties		5,300,000	5,800,000	5,000,000
Maintenance expenses – third parties		3,400,000	1,500,000	2,600,000
Maintenance expenses – related parties		400,000	300,000	100,000
General and administrative – third parties		2,400,000	2,800,000	4,600,000
General and administrative – related parties		14,500,000	14,100,000	14,100,000
Depreciation		2,500,000	2,600,000	2,700,000
Impairment and other, net		0	1,000,000	0
Property and other taxes		700,000	700,000	500,000
Total costs and expenses		43,500,000	43,000,000	41,100,000
Operating income		85,400,000	85,500,000	75,300,000
Income from equity method investments		110,800,000	116,700,000	94,400,000
Interest expense, net		7,900,000	15,100,000	4,000,000
Net income		188,300,000	187,100,000	165,700,000
Less: Net income attributable to non-controlling interests		19,900,000	19,200,000	32,600,000
Net income attributable to the Partnership	$ 133,100,000	168,400,000	167,900,000	133,100,000
Limited Partners Common Units
Costs and expenses
Net income attributable to the Partnership		$ 81,800,000	$ 82,700,000	66,600,000
Net income attributable to the Partnership per limited partner unit – basic and diluted (in dollars):
Net income per limited partnership unit, basic and diluted (in dollars per share)	$ 1.27	$ 1.56	$ 1.58
Limited Partners Subordinated Units
Costs and expenses
Net income attributable to the Partnership		$ 81,800,000	$ 82,700,000	$ 66,500,000
Net income attributable to the Partnership per limited partner unit – basic and diluted (in dollars):
Net income per limited partnership unit, basic and diluted (in dollars per share)	$ 1.27	$ 1.56	$ 1.58
Common Units Public
Weighted Average Number of Limited Partner Units Outstanding - Basic and Diluted (in millions):
Weighted average number of limited partner units outstanding (in dollars per share)	47.8	47.8	47.8
BP Holdco | Common Units
Weighted Average Number of Limited Partner Units Outstanding - Basic and Diluted (in millions):
Weighted average number of limited partner units outstanding (in dollars per share)	4.6	4.6	4.6
BP Holdco | Subordinated Units
Weighted Average Number of Limited Partner Units Outstanding - Basic and Diluted (in millions):
Weighted average number of limited partner units outstanding (in dollars per share)	52.4	52.4	52.4

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Non-controlling Interests	Common UnitsPartners' CapitalGeneral Public	Common UnitsPartners' CapitalGeneral PublicCumulative Effect, Period of Adoption, Adjustment	Common UnitsPartners' CapitalBP Holdco	Common UnitsPartners' CapitalBP HoldcoCumulative Effect, Period of Adoption, Adjustment	Subordinated UnitsPartners' CapitalBP Holdco	Subordinated UnitsPartners' CapitalBP HoldcoCumulative Effect, Period of Adoption, Adjustment	General PartnerPartners' Capital
Beginning Balance at Dec. 31, 2017	$ 580,800	$ (2,800)	$ 342,300	$ 824,600	$ (1,300)	$ (47,200)	$ (100)	$ (538,900)	$ (1,400)	$ 0
Net income	165,700		32,600	60,700		5,900		66,500
Distributions	(105,900)			(48,300)		(4,700)		(52,900)
Acquisitions from Parent	(380,800)		(187,600)	900		(15,600)		(178,500)
Unit-based compensation	200			200
Distributions to non-controlling interests	(46,400)		(46,400)
Ending Balance at Dec. 31, 2018	210,800		140,900	836,800		(61,700)		(705,200)		0
Net income	187,100		19,200	75,500		7,200		82,700		2,500
Distributions	(134,700)			(60,900)		(5,800)		(66,700)		(1,300)
Unit-based compensation	200			200
Distributions to non-controlling interests	(23,200)		(23,200)
Ending Balance at Dec. 31, 2019	240,200		136,900	851,600		(60,300)		(689,200)		1,200
Net income	188,300		19,900	74,700		7,100		81,800		4,800
Distributions	(150,400)			(66,400)		(6,400)		(72,800)		4,800
Unit-based compensation	200			200
Distributions to non-controlling interests	(24,300)		(24,300)
Ending Balance at Dec. 31, 2020	$ 254,000		$ 132,500	$ 860,100		$ (59,600)		$ (680,200)		$ 1,200

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities
Net income	$ 188,300,000	$ 187,100,000	$ 165,700,000
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation	(2,500,000)	(2,600,000)	(2,700,000)
Impairment and other, net	0	1,000,000	0
Non-cash expenses	200,000	300,000	200,000
Income from equity method investments	(110,800,000)	(116,700,000)	(94,400,000)
Distributions of earnings received from equity method investments	112,300,000	119,900,000	98,100,000
Changes in operating assets and liabilities
Accounts receivable	700,000	(1,800,000)	(400,000)
Prepaid expenses and other current assets	(1,400,000)	(500,000)	(3,300,000)
Accounts payable	900,000	(2,400,000)	800,000
Deferred revenues and credits – related parties	300,000	400,000	1,100,000
Other	(2,600,000)	(600,000)	3,300,000
Net cash provided by operating activities	190,400,000	189,300,000	173,800,000
Cash flows from investing activities
Capital expenditures	(3,500,000)	(1,100,000)	(1,600,000)
Acquisitions from Parent	0	0	(87,200,000)
Distribution in excess of earnings from equity method investments	13,000,000	11,500,000	19,600,000
Net cash provided by (used in) investing activities	12,400,000	10,400,000	(69,200,000)
Cash flows from financing activities
Proceeds from issuance of debt – related parties	468,000,000	0	468,000,000
Repayment of debt – related parties	(468,000,000)	0	(15,000,000)
Distribution of IPO proceeds to our Parent	0	0	(200,000)
Acquisitions from Parent	0	0	(380,800,000)
Distributions to unitholders and general partner	(150,400,000)	(134,700,000)	(105,900,000)
Distributions to non-controlling interests	(24,300,000)	(23,200,000)	(46,400,000)
Net cash used in financing activities	(174,700,000)	(157,900,000)	(80,300,000)
Net change in cash and cash equivalents	28,100,000	41,800,000	24,300,000
Cash and cash equivalents at beginning of the year	98,800,000	57,000,000	32,700,000
Cash and cash equivalents at end of the year	126,900,000	98,800,000	57,000,000
Supplemental cash flow information
Cash paid for interest	11,600,000	16,400,000	700,000
Operating Lease, Payments	100,000	100,000	0
Non-cash investing and financing transactions:
Accrued capital expenditures	$ 4,100,000	$ 200,000	$ 200,000

Business and Basis of Presentat

Business and Basis of Presentation	12 Months Ended
	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business and Basis of Presentation	Business and Basis of Presentation BP Midstream Partners LP (either individually or together with its subsidiaries, as the context requires, the “Partnership”) is a Delaware limited partnership formed on May 22, 2017 by BP Pipelines (North America) Inc. (“BP Pipelines”), an indirect wholly owned subsidiary of BP p.l.c. (“BP”), a “foreign private issuer” within the meaning of the Securities Exchange Act of 1934, as amended. On October 30, 2017, the Partnership completed its initial public offering (the "IPO") of common units representing limited partner interests. Unless otherwise stated or the context otherwise indicates, all references to “we,” “our,” “us,” or similar expressions refer to the legal entity BP Midstream Partners LP. The term “our Parent” refers to BP Pipelines; any entity that wholly owns BP Pipelines, indirectly or directly, including BP and BP America Inc. (“BPA”), an indirect wholly owned subsidiary of BP; and any entity that is wholly owned by the aforementioned entities, excluding BP Midstream Partners LP. Business BP Midstream Partners LP is a master limited partnership formed by BP Pipelines to own, operate, develop and acquire pipelines and other midstream assets. The Partnership's assets consist of interests in entities that own crude oil, natural gas, refined products and diluent pipelines and refined product terminals serving as key infrastructure for BP and other customers to transport onshore crude oil production to BP’s refinery in Whiting, Indiana (the "Whiting Refinery") and offshore crude oil and natural gas production to key refining markets and trading and distribution hubs. Certain assets deliver refined products and diluent from the Whiting Refinery and other U.S. supply hubs to major demand centers. As of December 31, 2020, the Partnership's assets consisted of the following: • BP Two Pipeline Company LLC, which owns the BP#2 crude oil pipeline system (“BP2”). • BP River Rouge Pipeline Company LLC, which owns the Whiting to River Rouge refined products pipeline system (“River Rouge”). • BP D-B Pipeline Company LLC, which owns the Diamondback diluent pipeline system (“Diamondback”). BP2, River Rouge, and Diamondback, together, are referred to as the "Wholly Owned Assets". • 28.5% ownership interest in Mars Oil Pipeline Company, LLC (“Mars”), which owns a major corridor crude oil pipeline system in the Gulf of Mexico. • 65% ownership interest and 100% managing member interest in Mardi Gras Transportation System Company, LLC (“Mardi Gras”), which holds the following investments in joint ventures located in the Gulf of Mexico: • 56% ownership interest in Caesar Oil Pipeline Company, LLC (“Caesar”), • 53% ownership interest in Cleopatra Gas Gathering Company, LLC (“Cleopatra”), • 65% ownership interest in Proteus Oil Pipeline Company, LLC (“Proteus”), and, • 65% ownership interest in Endymion Oil Pipeline Company, LLC (“Endymion”). • Together Endymion, Caesar, Cleopatra and Proteus are referred to as the “Mardi Gras Joint Ventures.” • 22.7% ownership interest in Ursa Oil Pipeline Company, LLC ("Ursa"). • 25% ownership interest in KM Phoenix Holdings, LLC ("KM Phoenix"). We generate a majority of revenue by charging fees for the transportation of crude oil, refined products and diluent through our pipelines under agreements with minimum volume commitments ("MVC"). We do not engage in the marketing and trading of any commodities. All operations are conducted in the United States, and all long-lived assets are located in the United States. Partnership operations consist of one reportable segment. Certain Partnership businesses are subject to regulation by various authorities including, but not limited to FERC. Regulatory bodies exercise statutory authority over matters such as common carrier tariffs, construction, rates and ratemaking and agreements with customers. Basis of Presentation Consolidated financial statements have been prepared under the rules and regulations of the Securities and Exchange Commission (“SEC”). These rules and regulations conform to the accounting principles contained in the Financial Accounting

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Principles of Consolidation Our consolidated financial statements include all subsidiaries, where the Partnership has control and a variable interest entity ("VIE") of which we are the primary beneficiary. The assets and liabilities in the consolidated financial statements have been reflected on a historical basis. All inter-company accounts and transactions are eliminated upon consolidation. We evaluate our ownership, contractual arrangements and other interests in entities to determine if these entities are VIEs and whether we are the primary beneficiary of the VIE. In determining whether we are the primary beneficiary of a VIE and therefore required to consolidate the VIE, we apply a qualitative approach that determines whether we have both (1) the power to direct the activities of the VIE that most significantly impact the economic performance and (2) the obligation to absorb the majority of losses of or the rights to receive the majority of the benefits from the VIE that could potentially be significant to the VIE. We continuously assess whether we are the primary beneficiary of a VIE as changes to existing relationships or future transactions may result in the consolidation or deconsolidation, as the case may be, of such VIE. We consolidate BP2, River Rouge and Diamondback, as we control these entities through 100% of the ownership interest. We control and consolidate Mardi Gras via an agreement between us and our Parent, under which we have the right to vote 100% of Mardi Gras' interests in each of the Mardi Gras Joint Ventures. We have determined that we are the primary beneficiary of Mardi Gras. Refer to Note 16 - Variable Interest Entity for further discussion. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported on the consolidated financial statements and disclosures included in the accompanying notes. Actual results could differ from these estimates. Common Control Transactions Assets and businesses acquired from our Parent and its subsidiaries are accounted for as common control transactions whereby the net assets acquired are included in our consolidated balance sheets at their historical carrying value. If any recognized consideration transferred in such a transaction exceeds the historical carrying value of the net assets acquired, the excess is treated as a capital distribution to our Parent, similar to a dividend. If the historical carrying value of the net assets acquired exceeds any recognized consideration transferred including, if applicable, the fair value of any limited partner units issued, such excess is treated as a capital contribution from our Parent. Revenue Recognition We recognize revenue at an amount that reflects the consideration to which we expect to be entitled in exchange for transferring goods or services to a customer. We include certain disclosures regarding qualitative and quantitative information regarding the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. Refer to Note 4 - Revenue Recognition for further information. Equity Method Investments We account for an investment under the equity method if we have the ability to exercise significant influence, but not control, over the investee. Under the equity method of accounting, the investment is recorded at its initial carrying value on the consolidated balance sheets and is adjusted for capital contributions, dividends received and our share of the investee’s earnings or losses, which is recorded as a component of Income from equity method investments on the consolidated statements of operations. We evaluate equity method investments for impairment when events or changes in circumstances indicate, in our management’s judgment, that a decline in value is other than temporary. Factors that may indicate that a decline in value is other than temporary include a deterioration in the financial condition of the investee, decisions to sell the investee, significant losses incurred by the investee, a change in the economic environment that is expected to adversely affect the investee’s operations, an investee’s loss of a principal customer or supplier and an investee’s recording of impairment charges. If we determine that a decline in value is other than temporary, the investment is written down to its fair value, which establishes the investment’s new cost basis. Property, plant and equipment Our property, plant and equipment is recorded at its historical cost of construction, or the carrying value of the transferring entity in a transaction under common control, or at fair value in a business combination. We record depreciation using the straight-line method with the following useful lives: Depreciable Land — ROW assets — Buildings and improvements 16 - 40 Pipelines and equipment 17 - 40 Other 4 - 23 Construction in progress — Upon the sale or retirement of property, plant and equipment, the cost and related accumulated depreciation are removed, and any resulting gain or loss is recorded on the consolidated statements of operations. Ordinary maintenance and repair costs are generally expensed as incurred. Such costs are recorded in Maintenance expenses- third parties and Maintenance expenses-related parties on our consolidated statements of operations. Costs of major renewals, betterments and replacements are capitalized as Property, plant and equipment. For constructed assets, we capitalize all construction-related direct labor and material costs, as well as indirect construction costs. Impairment of Long-lived Assets We evaluate long-lived assets of identifiable business activities for impairment when events or changes in circumstances indicate, in our management’s judgment, that the carrying value of such assets may not be recoverable. These events include market declines that are believed to be other than temporary, changes in the manner in which we intend to use a long-lived asset, decisions to sell an asset and adverse changes in the legal or business environment, such as adverse actions by regulators. If an event occurs, which is a determination that involves judgment, we evaluate the recoverability of our carrying values of an asset group based on the long-lived assets’ ability to generate future cash flows on an undiscounted basis. If the carrying amount is higher than the undiscounted cash flows, we further evaluate the impairment loss by comparing management’s estimate of the fair value of the assets to the carrying value of such assets. We record a loss for the amount that the carrying value exceeds the estimated fair value. Cash Equivalents Cash equivalents are highly liquid, short-term investments that are readily convertible to known amounts of cash and will mature within 90 days or less from the date of acquisition. We record cash equivalents, if any, at its carrying value, which approximates its fair value. Accounts Receivable and Allowance for Doubtful Accounts Accounts receivable represent valid claims against customers for services rendered, net of allowances for doubtful accounts. We assess the creditworthiness of our counterparties on an ongoing basis and require security, including prepayments and other forms of collateral, when appropriate. Our policy is to establish provisions for losses on accounts receivable due from shippers if we determine that we will not collect all or part of the outstanding balance. Outstanding customer receivables are regularly reviewed for possible nonpayment indicators, and allowances for doubtful accounts are recorded based upon management’s estimate of collectability based on a historical analysis of uncollected amounts, general and specific economic trends, known specific issues related to individual customers, sectors and transactions that might impact collectability at each balance sheet date. At December 31, 2020 and 2019, more than 95% of our accounts receivable are with a related party and we have not experienced any significant collection issues and do not expect collection issues in the foreseeable future; therefore, we have recorded zero in allowance for doubtful accounts. Income Taxes BP Midstream Partners LP is treated as a partnership for federal and state income tax purposes, with each partner being separately taxed on its share of taxable income. We are not subject to U.S. federal income taxes. Rather, our taxable income flows through to the owners, who are responsible for paying the applicable income taxes on the income allocated to them. For tax years beginning on or after January 1, 2018, we are subject to partnership audit rules enacted as part of the Bipartisan Budget Act of 2015 (the “Centralized Partnership Audit Regime”). Under the Centralized Partnership Audit Regime, any IRS audit of the Partnership would be conducted at the Partnership level, and if the IRS determines an adjustment, the default rule is that we would pay an “imputed underpayment” including interest and penalties, if applicable. We may instead elect to make a “push-out” election, in which case the partners for the year that is under audit would be required to take into account the adjustments on their own personal income tax returns. Our partnership agreement does not stipulate how we will address imputed underpayments. If we receive an imputed underpayment, a determination will be made based on the relevant facts and circumstances that exist at that time. We may treat any payments of imputed underpayment, which are made on behalf of our unitholders, as distribution of cash to such unitholders. Asset Retirement Obligations Asset retirement obligations represent legal and constructive obligations associated with the retirement of long-lived assets that result from the acquisition, construction, development and/or normal use of the asset. We record liabilities for obligations related to the retirement and removal of long-lived assets used in our businesses at fair value on a discounted basis when they are incurred and can be reasonably estimated. Amounts recorded for the related assets are increased by the amount of these obligations. Over time, the liabilities increase due to the change in their present value, and the initial capitalized costs are depreciated over the useful lives of the related assets. The liabilities are eventually extinguished when settled at the time the asset is taken out of service. Although the Wholly Owned Assets will be replaced as needed, in management's judgement, the pipelines will continue to exist for an indefinite period of time. Therefore, there is uncertainty around the asset retirement settlement dates. As a result, we determined that there is not sufficient information to make a reasonable estimate of the asset retirement obligations for the Wholly Owned Assets, and we did not recognize any asset retirement obligations as of December 31, 2020 and 2019. We continue to evaluate our asset retirement obligations and future developments that could impact the amounts we record. Legal We are subject to litigation and regulatory proceedings as the result of our business operations and transactions. We utilize both internal and external counsel in evaluating our potential exposure to adverse outcomes from orders, judgments or settlements. In general, we expense legal costs as incurred. Environmental Matters We are subject to federal, state, and local environmental laws and regulations. These laws require us to take future action to remediate the effects on the environment of prior disposal or release of chemicals or petroleum substances by us or other parties. Environmental expenditures that are required to obtain future economic benefits from its assets are capitalized as part of those assets. Expenditures that relate to an existing condition caused by past operations and that do not contribute to current or future earnings shall be expensed, unless already provisioned for, which then shall be charged against provisions. Provisions are recognized when we have a present legal or constructive obligation as a result of a past event, if it is probable that an outflow of resources embodying economic benefits will be required to settle the obligation and a reliable estimate can be made of the amount of the obligation. We do not discount environmental liabilities, and we record environmental liabilities when environmental assessments and/or remedial efforts are probable, and when we can reasonably estimate the costs. In making environmental liability estimations, we consider the material effect of environmental compliance, pending legal actions against us and potential third-party liability claims. Often, as the remediation evaluation and effort progresses, additional information is obtained, requiring revisions to estimated costs. Generally, our recording of these provisions coincides with our commitment to a formal plan of action, or if earlier, on the closure or divestment of inactive sites. We recognize receivables for anticipated associated insurance recoveries when such recoveries are deemed to be probable. The ultimate requirement for remediation and its cost are inherently difficult to estimate. We believe that the outcome of these uncertainties should not have a material adverse effect on our financial condition, cash flows, or operating results. Our existing environmental conditions prior to the IPO are obligations contributed to us by the prior operator of these facilities, BP Pipelines, who has agreed to indemnify us with respect to such conditions under the terms of an omnibus agreement that we entered into in connection with the IPO. For provisions related to such conditions, we record indemnification assets in our consolidated balance sheets in the amounts that equal the provisions. Subsequent to the IPO, revisions to the estimated environmental liability for conditions that are not indemnified under the omnibus agreement with our Parent are reflected in our consolidated statements of operations when they are probable and reasonably estimable. For additional information regarding our environmental matters, refer to Note 13 - Commitments and Contingencies . Other Contingencies We recognize liabilities for contingencies when we have an exposure that indicates it is both probable that a liability has been incurred and the amount of loss can be reasonably estimated. Where the most likely outcome of a contingency can be reasonably estimated, we accrue a liability for that amount. Where the most likely outcome cannot be estimated, a range of potential losses is established and if no one amount in that range is more likely than any other, the lower end of the range is accrued. To the extent that actual outcomes differ from our estimates, or additional facts and circumstances cause us to revise our estimates, our earnings will be affected. Fair Value Estimates Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. We categorize assets and liabilities measured at fair value into one of three levels depending on the ability to observe inputs employed in their measurement: • Level 1 inputs are quoted prices in active markets for identical assets or liabilities. • Level 2 inputs are inputs that are observable, either directly or indirectly, other than quoted prices included within level 1 for the asset or liability. • Level 3 inputs are unobservable inputs for the asset or liability reflecting significant modifications to observable related market data or our assumptions about pricing by market participants. We classify the fair value of an asset or liability based on the lowest level of input significant to its measurement. A fair value initially reported as Level 3 will be subsequently reported as Level 2 if the unobservable inputs become inconsequential to its measurement, or corroborating market data becomes available. Asset and liability fair values initially reported as Level 2 will be subsequently reported as Level 3 if corroborating market data becomes unavailable. Net Income per Unit Net income per unit applicable to common limited partner units and to subordinated limited partner units is computed by dividing the respective limited partners’ interest in net income by the weighted average number of common units and subordinated units, respectively, outstanding for the period. Because we have more than one class of participating securities, we use the two-class method when calculating the net income per unit applicable to limited partners. The classes of participating securities include common units, subordinated units and incentive distribution rights. Unit-Based Compensation The fair value of phantom unit awards granted to non-employee directors is based on the fair market value of our common units on the date of grant. Our unit-based compensation expenses are recognized ratably over the vesting term of the awards. We have elected to recognize the impact of forfeitures only when they occur. Leases We recognize an operating lease right-of-use (“ROU”) asset and a corresponding operating lease liability on our consolidated balance sheets based on the present value of the future minimum lease payments over the lease term at commencement date for arrangements with duration greater than one year. We use our incremental borrowing rate to determine the present value of future minimum lease payments over the duration of the lease term, which is determined to be reasonably certain. We do not separate lease and non-lease components for accounting purposes.

Acquisitions

Acquisitions	Oct. 30, 2017
Business Combinations [Abstract]
Acquisitions	Acquisitions Acquisition of Equity Interests On October 1, 2018, pursuant to an Interest Purchase Agreement (the “Interest Purchase Agreement”) with BP Products North America Inc. (“BP Products”), BP Offshore Pipelines Company LLC (“BP Offshore”), and BP Pipelines completed the acquisition of: • (i) an additional 45.0% interest in Mardi Gras, from BP Pipelines, which brought our ownership interest to 65.0%, • (ii) a 22.7% interest in Ursa, from BP Offshore, and • (iii) a 25% interest in KM Phoenix, from BP Products. These assets were acquired in exchange for aggregate consideration of $468.0 million funded with borrowings under our revolving credit facility. The purchase was accounted for as an acquisition of assets between entities under common control; as a result, we recognized the acquired assets at their historical carrying value. The consideration paid is reported in our consolidated statements of cash flows as $380.8 million in financing activities for the distributions to our Parent for the acquisition of the non-controlling interest in Mardi Gras and excess of the purchase price over the carrying value for other assets acquired and $87.2 million in investing activities for the remainder. For more details, refer to the consolidated statements of cash flows.

Revenue Recognition

Revenue Recognition	12 Months Ended
	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Revenue Recognition	Revenue Recognition We recognize revenue over time or at a point in time, depending on the nature of the performance obligations contained in the respective contract with customers. A performance obligation is our unit of account and it represents a promise in a contract to transfer goods or services to the customer. The contract transaction price, which is the amount of consideration to which an entity expects to be entitled in exchange for transferring promised goods or services to a customer, is allocated to each performance obligation and recognized as revenue when or as the performance obligation is satisfied. The following is an overview of our significant revenue stream, including a description of the respective performance obligations and related methods of revenue recognition. Pipeline Transportation Revenue from pipeline transportation is comprised of tariffs and fees associated with the transportation of liquid petroleum products, generally at published tariffs and in certain instances, revenue from MVC contracts at negotiated rates. Tariff revenue is recognized either at the point of delivery or at the point of receipt, pursuant to specifications outlined in the respective tariffs. We record revenue for crude oil, refined products and diluent transportation during the period in which they are earned (i.e., either physical delivery of product has taken place or the services designated in the contract have been performed). Partnership services are typically billed on a monthly basis, and we generally do not offer extended payment terms. We accrue revenue based on services rendered but not billed for that accounting month. Billings to BP Products for deficiency volumes under its MVCs, if any, are recorded as deferred revenue and credits, a contract liability, on the consolidated balance sheets, as BP Products has the right to make up the deficiency volumes within the measurement period specified by the agreements. Deferred revenue under these arrangements is recognized into revenue once it is deemed remote that the customer will meet its required annual MVC. If the customer does satisfy its MVC by shipping the deficiency volumes within the same calendar year, it may receive a refund of excess payments. We recognized $13.2 million, $5.6 million and $8.0 million of deficiency revenue under the throughput and deficiency agreements with BP Products for the years ended December 31, 2020, 2019 and 2018, respectively. Allowance Oil The tariff for crude oil transportation at BP2 includes a fixed loss allowance (“FLA”). An FLA factor per barrel, a fixed percentage, is a separate fee that is considered a part of the transaction price under the applicable crude oil tariff to cover evaporation and other losses in transit. The amount of revenue recognized is a product of the quantity transported, the applicable FLA factor and the settlement price during the month the product is transported. The settlement price for volumes accumulated is determined using a summation of the calendar-month average of West Texas Intermediate (“WTI”) on the New York Mercantile Exchange with pricing input from the month of movement, pursuant to a related party agreement that we entered into with our affiliate. The settlement price is fixed and determinable upon the completion of transportation. We settle the allowance oil at the end of each period. The balances are entirely recorded in Accounts receivable - related parties in the consolidated balance sheets. In the years ended December 31, 2020, 2019 and 2018, we recognized revenue o f $5.8 million, $10.3 million and $8.8 million, respectively, related to the FLA arrangements with our Parent. Disaggregation of Revenue The following table provides information about disaggregated revenue: Year Ended December 31, Disaggregation of revenue 2020 2019 2018 Transportation services revenue - third parties 2.9 $ 3.0 $ 2.8 Transportation services revenue - related parties 126.0 125.5 113.6 Total revenue $ 128.9 $ 128.5 $ 116.4 Future Performance Obligations The values in the table below represent the fixed portion of the MVC arrangements with our existing customer contracts, summarized as future performance obligations as of December 31, 2020. The unfulfilled performance obligations included in the table below are expected to be recognized in revenue in the specified periods: Unfulfilled performance obligations As of December 31, 2020 2021 $ 106.0 2022 102.2 2023 98.4 Total $ 306.6 Contract Balances Contract assets and contract liabilities are the result of timing differences between revenue recognition, billings and cash collections. Contract liabilities or deferred revenue and credits primarily relate to consideration received from customers for temporary deficiency quantities under minimum volume contracts that the customer has the right to make up in a future period, which we subsequently recognize as revenue or amounts we credit back to the customer in a future period. The following table provides information about receivables from contracts with customers, contract assets and contract liabilities: As of December 31, Contract balances 2020 2019 Receivables from contracts with customers - third parties $ 0.2 $ 0.6 Receivables from contracts with customers - related parties 11.0 11.3 Deferred revenue and credits - related parties 1.8 1.5 Deferred revenue and credits on our consolidated balance sheets as of December 31, 2020 and 2019 were credited to customers' invoices in January 2021 and January 2020, respectively.

Leases, Codification Topic 842

Leases, Codification Topic 842	Jan. 01, 2019
Leases [Abstract]
Lessee, Operating Leases	Leases Beginning January 1, 2019, operating ROU assets and operating lease liabilities are recognized based on the present value of lease payments over the lease term at commencement date. Because our leases do not provide an explicit rate of return, we use our incremental borrowing rate based on lease term information available at the commencement date in determining the present value of lease payments. We have a total of four operating leases related to office space of which the term of two expires in 2036 and the other two in 2023. We have the option to terminate our leases 30 days after providing written notice of the election to terminate to the landlord. Two of our leases include a right of renewal and an annual 3% escalation on the anniversary date of lease inception. We have the option to renew our leases by giving notice to landlord not less than 60 days prior to the expiration of the lease term. We have not included the option to renew the leases in our determination of lease term because at the time of lease inception it was not certain we would exercise the renewal. We have included the variable lease payments based on the escalation percentage from above in the determination of our lease liabilities and our ROU assets. The other two leases include a non-lease component for maintenance expense. No leases include a residual value guarantee or provide us an option to acquire the real property at the end of the lease. We have no material subleasing arrangements. For the years ended December 31, 2020, 2019 and 2018, lease expense totaled $71 thousand, $71 thousand and $61 thousand, respectively. In November 2020, two operating leases were renewed, and lease terms were extended until 2023, resulting in additional ROU assets and lease liabilities of $94 thousand. Amounts recognized in the accompanying consolidated balance sheets are as follows: Lease activity (in thousands) Balance sheet location December 31, 2020 December 31, 2019 ROU assets Other assets $ 513 $ 469 Current lease liability Other current liabilities $ 62 $ 60 Long-term lease liability Other liabilities $ 467 $ 417 As of December 31, 2020, the weighted average discount rate of our leases was 4.0% and the weighted average remaining lease term was 13.2 years. The undiscounted future minimum lease payments and total lease liabilities as of December 31, 2020 are presented in the table below: (In thousands) December 31, 2020 2021 $ 64 2022 65 2023 66 2024 35 2025 36 Remaining years 443 Undiscounted future minimum lease payments 709 Less: Interest (180) Total lease liabilities $ 529

Equity Method Investments

Equity Method Investments	12 Months Ended
	Dec. 31, 2020
Equity Method Investments and Joint Ventures [Abstract]
Equity Method Investments	Equity Method Investments We account for our ownership interests in Mars, Ursa, KM Phoenix and the Mardi Gras Joint Ventures using the equity method for financial reporting purposes. Our financial results include our proportionate share of the net income of Mars, Ursa, KM Phoenix and the Mardi Gras Joint Ventures, which is reflected in Income from equity method investments on the consolidated statements of operations. We did not record any impairment loss on our equity method investments during the years ended 2020, 2019 or 2018. The table below summarizes the balances and activities related to each of our equity method investments ("EMI") that we recorded for the years ended December 31, 2020, 2019 and 2018: 2020 Percentage ownership at year end Distributions received Income from EMI Carrying value at year end Mars 28.5 % $ (49.1) $ 46.3 $ 54.1 Caesar (1) 56.0 % (16.1) 15.2 116.5 Cleopatra (1) 53.0 % (8.9) 5.6 114.3 Proteus (1) 65.0 % (20.5) 13.6 68.4 Endymion (1) 65.0 % (24.3) 22.6 79.3 Others (2) Various (6.4) 7.5 87.3 Total Equity Investments $ (125.3) $ 110.8 $ 519.9 2019 Percentage ownership at year end Distributions received Income from EMI Carrying value at year end Mars 28.5 % $ (53.4) $ 51.1 $ 56.9 Caesar (1) 56.0 % (19.5) 17.5 117.4 Cleopatra (1) 53.0 % (11.0) 9.0 117.6 Proteus (1) 65.0 % (19.0) 13.0 75.3 Endymion (1) 65.0 % (16.8) 15.3 81.0 Others (2) Various (11.7) 10.8 86.2 Total Equity Investments $ (131.4) $ 116.7 $ 534.4 2018 Percentage ownership at year end Cumulative effect of accounting change (3) Distributions received Income from EMI Carrying value at year end Mars 28.5 % $ (2.8) $ (47.5) $ 43.9 $ 59.1 Caesar (1) 56.0 % — (21.0) 16.8 119.4 Cleopatra (1) 53.0 % — (10.5) 6.5 119.6 Proteus (1) 65.0 % — (18.1) 12.3 81.3 Endymion (1) 65.0 % — (18.0) 12.3 82.5 Others (2) Various — (2.7) 2.6 87.1 Total Equity Investments $ (2.8) $ (117.8) $ 94.4 $ 549.0 (1) These investments are held by our investment in Mardi Gras which increased to 65% from 20% on October 1, 2018. See Note 3 - Acquisitions for further detail. (2) Includes ownership interest in Ursa (22.7%) and KM Phoenix (25%) acquired on October 1, 2018. (3) The financial results of Mars reflect the adoption of FASB Accounting Standards Codification Topic 606 “Revenue from Contracts with Customers” on January 1, 2018 under the modified retrospective transition method through a cumulative adjustment to equity. Our cumulative effect impact from this accounting change to our Mars investment was $(2.8) million, offset to equity. The Mardi Gras Joint Ventures and Ursa adopted this ASU on January 1, 2019, and there was no cumulative effect impact from the adoption. KM Phoenix adopted Topic 606 on January 1, 2018, and there was no cumulative effect impact from the adoption. The following tables present aggregated selected balance sheet and income statement data for our equity method investments on a 100% basis for the years ended December 31, 2020, 2019 and 2018 and as of December 31, 2020 and 2019: For the Year Ended December 31, 2020 2019 2018 Statement of operations Revenue $ 538.6 $ 560.5 $ 470.8 Operating expenses 250.2 246.0 200.9 Net income 288.9 317.2 270.4 As of December 31, Balance Sheets 2020 2019 Current assets 110.8 128.7 Non current assets 1,726.4 1,630.7 Current liabilities 56.5 49.6 Non current liabilities 589.4 493.0 Equity 1,191.3 1,216.8

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, Plant and Equipment Property, plant and equipment consisted of the following: December 31, 2020 2019 Land $ 0.2 $ 0.2 Rights-of-way assets 1.4 1.4 Buildings and improvements 6.9 6.9 Pipelines and equipment 95.3 94.4 Other 0.8 0.5 Construction in progress 7.1 0.6 Property, plant and equipment 111.7 104.0 Less: Accumulated depreciation (43.8) (41.3) Property, plant and equipment, net $ 67.9 $ 62.7 During the year ended December 31, 2019, an impairment charge of $4.4 million, before insurance recoveries, was recorded under "Impairment and other, net" on our consolidated statements of operations. See Note 13 - Commitments and Contingencies .

Accrued Liabilities

Accrued Liabilities	12 Months Ended
	Dec. 31, 2021
Payables and Accruals [Abstract]
Accrued Liabilities	Liabilities Other current liabilities consist of the following: December 31, 2020 2019 Accrued capital expenditures $ 4.1 $ 0.2 Accrued interest payable - related parties 0.9 4.2 Current portion of environmental remediation obligation 0.4 0.6 Current portion of lease liabilities 0.1 0.1 Accrued liabilities 2.3 1.5 Other current liabilities $ 7.8 $ 6.6

Debt

Debt	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Debt	Debt On October 30, 2017, the Partnership entered into a $600.0 million unsecured revolving credit facility agreement (the “credit facility”) with an affiliate of BP. The credit facility terminates on October 30, 2022 and provides for certain covenants, including the requirement to maintain a consolidated leverage ratio, which is calculated as total indebtedness to consolidated EBITDA (as defined in the credit facility), not to exceed 5.0 to 1.0, subject to a temporary increase in such ratio to 5.5 to 1.0 in connection with certain material acquisitions. In addition, the limited liability company agreement of the Partnership's general partner requires the approval of BP Holdco prior to the incurrence of any indebtedness that would cause the Partnership's leverage ratio to exceed 4.5 to 1.0. The credit facility also contains customary events of default, such as (i) nonpayment of principal when due, (ii) nonpayment of interest, fees or other amounts, (iii) breach of covenants, (iv) misrepresentation, (v) cross-payment default and cross-acceleration (in each case, to indebtedness in excess of $75.0 million) and (vi) insolvency. Additionally, the credit facility limits our ability to, among other things: (i) incur or guarantee additional debt, (ii) redeem or repurchase units or make distributions under certain circumstances; and (iii) incur certain liens or permit them to exist. Indebtedness under this facility bears interest at the 3-month LIBOR plus 0.85%. Once a request to borrow is completed, our interest rate is fixed through the maturity date of the borrowing, typically six months. This facility includes customary fees, including a commitment fee of 0.10% and a utilization fee of 0.20%. There is no debt issuance cost associated with the credit facility. On October 1, 2018, the Partnership borrowed $468.0 million under the credit facility to fund our acquisition. On February 24, 2020, the Partnership entered into a $468.0 million Term Loan Facility Agreement ("term loan") with an affiliate of BP. On March 13, 2020, proceeds were used to repay outstanding borrowings under the existing credit facility. The term loan has a final repayment date of February 24, 2025, and provides for certain covenants, including the requirement to maintain a consolidated leverage ratio, which is calculated as total indebtedness to consolidated EBITDA, not to exceed 5.0 to 1.0, subject to a temporary increase in such ratio to 5.5 to 1.0 in connection with certain material acquisitions. Simultaneous with this transaction, we entered into a First Amendment to Short Term Credit Facility Agreement ("First Amendment") whereby the lender added a provision that indebtedness under both the term loan and credit facility shall not exceed $600.0 million. All other terms of the credit facility remain the same. As of December 31, 2020, the Partnership was in compliance with the covenants contained in the credit facility and term loan. The weighted average interest rate for our long-term debt was 1.70% and 3.25% at December 31, 2020 and 2019, respectively. For the years ended December 31, 2020, 2019 and 2018, interest and fees incurred were $8.3 million, $16.5 million and $4.8 million, respectively.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2020
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions Related party transactions include transactions with our Parent and our Parent’s affiliates, including those entities in which our Parent has an ownership interest but does not have control. In addition to the fixed loss allowance arrangements discussed in Note 4 - Revenue Recognition and the credit facilities in Note 9 - Debt , we have entered into the following transactions with our related parties: Omnibus Agreement The Partnership has entered into an omnibus agreement with BP Pipelines and certain of its affiliates, including the general partner. This agreement addresses, among other things, (i) the Partnership's obligation to pay an annual fee for general and administrative services provided by BP Pipelines and its affiliates, (ii) the Partnership's obligation to reimburse BP Pipelines for personnel and other costs related to the direct operation, management and maintenance of the assets and (iii) the Partnership's obligation to reimburse BP Pipelines for services and certain direct or allocated costs and expenses incurred by BP Pipelines or its affiliates on behalf of the Partnership. Pursuant to the omnibus agreement, BP Pipelines will indemnify the Partnership and fund the costs of required remedial action for its known historical and legacy spills and releases and other environmental and litigation claims identified in the omnibus agreement. The omnibus agreement also addresses the Partnership's right of first offer to acquire BP Pipelines' retained ownership interest in Mardi Gras and all of BP Pipelines' interests in midstream pipeline systems and assets related thereto in the contiguous United States and offshore Gulf of Mexico that are owned by BP Pipelines at the closing of the IPO. Further, the omnibus agreement addresses the granting of a license from BPA to the Partnership with respect to use of certain BP trademarks and trade name. Related Party Revenue We provide crude oil, refined products and diluent transportation services to related parties and generate revenue through published tariffs. Effective July 1, 2017, we entered into a throughput and deficiency agreement with BP Products for transporting diluent on the Diamondback pipeline under two throughput and deficiency agreements and a dedication agreement. The dedication agreement with a third-party on Diamondback automatically renewed in 2021 and will now expire in June 2022. This contract is subject to successive one-year renewal periods at the election of the parties. The throughput and deficiency agreement for Diamondback automatically renewed in 2021 and will now expire in June 2022. On October 30, 2017, we entered into additional throughput and deficiency agreements with BP Products for each of our three wholly owned pipeline systems: BP2, River Rouge and Diamondback. Under these fee-based agreements, we provide transportation services to BP Products, in exchange for BP Products’ commitment to pay us the applicable tariff rates for the minimum monthly volumes, whether or not such volumes are physically shipped by BP Products through our pipelines. BP Products is allowed to make up for the monthly deficiency within the same calendar year during the initial term ending December 31, 2020. Adjustment to the monthly deficiency payments remitted to us by BP Products, if any, is determined at the end of each calendar year based on the actual volume transported during such period. These agreements expired on December 31, 2020. On November 3, 2020, the Partnership entered into throughput and deficiency agreements with BP Products with respect to volumes transported on BP2, River Rouge and Diamondback. These new agreements have a term of three years beginning January 1, 2021 and expiring December 31, 2023. Our revenue from related parties was $126.0 million, $125.5 million and $113.6 million for the years ended December 31, 2020, 2019 and 2018, respectively. We recognized $13.2 million, $5.6 million and $8.0 million of deficiency revenue under the throughput and deficiency agreements with BP Products for the years ended December 31, 2020, 2019 and 2018, respectively. At December 31, 2020 and 2019, there was $1.8 million and $1.5 million, respectively, of deferred revenue and credits recorded in relation to these agreements. Related Party Expenses All employees performing services on behalf of our operations are employees of our Parent. Our Parent also procures our insurance policies on our behalf and performs certain general corporate functions for us related to finance, accounting, treasury, legal, information technology, human resources, shared services, government affairs, insurance, health, safety, security, employee benefits, incentives, severance and environmental functional support. Personnel and operating costs incurred by our Parent on our behalf are included in either Operating expenses – related parties or General and administrative – related parties in the consolidated statements of operations, depending on the nature of the service provided. We paid our Parent an annual fee of $14.0 million, $13.6 million and $13.3 million in 2020, 2019 and 2018, respectively, under the omnibus agreement. The annual fee was adjusted to $15.2 million, payable in equal monthly installments, beginning on January 1, 2020. During the second quarter of 2020, our Parent agreed to adjust the fee payable under the Omnibus Agreement back to the 2019 annual fee, beginning in the second quarter, prorated for the remainder of 2020 due to the ongoing economic effects of the global COVID-19 pandemic. This resulted in a 2020 annual fee of $14.0 million. The annual fee was adjusted to $15.5 million per year, payable in equal monthly installments, beginning on January 1, 2021. Our general partner may adjust the administrative fee to reflect, among others, any change in the level or complexity of our operations, a change in the scope or cost of services provided to us, inflation or a change in law or other regulatory requirements, the contribution, acquisition or disposition of our assets or any material change in our operation activities. We also reimburse our Parent for personnel and other costs related to the direct operation, management and maintenance of the assets and services and certain direct or allocated costs and expenses incurred by our Parent or its affiliates on our behalf pursuant to the terms in the omnibus agreement. During the years ended December 31, 2020, 2019 and 2018, we recorded the following amounts for related party expenses, which also included the expenses related to pension and retirement savings plans and share-based compensation discussed below: Years Ended December 31, 2020 2019 2018 Operating expenses—related parties $ 5.3 $ 5.8 $ 5.0 Maintenance expenses—related parties 0.4 0.3 0.1 General and administrative—related parties 14.5 14.1 14.1 Total operating, maintenance, and general corporate costs—related parties $ 20.2 $ 20.2 $ 19.2 Non-controlling Interests Non-controlling interests consist of the 35% ownership interest in Mardi Gras held by our Parent at December 31, 2020, 2019 and 2018 compared to the 80% ownership interest held before completion of the acquisition on October 1, 2018.

Net Income Per Limited Partner

Net Income Per Limited Partner Unit	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Net Income Per Limited Partner Unit	Net Income Per Unit The following table details the distributions declared and/or paid for the periods presented: Three Months Ended Date Paid or General Partner** Limited Partners' Common Units Limited Partners' Subordinated Units Total Distributions per Limited Partner Unit (in dollars) December 31, 2017* February 15, 2018 $ — $ 9.4 $ 9.3 $ 18.7 $ 0.1798 March 31, 2018 May 15, 2018 — 14.0 14.0 28.0 0.2675 June 30, 2018 August 15, 2018 — 14.3 14.3 28.6 0.2725 September 30, 2018 November 15, 2018 — 15.3 15.3 30.6 0.2915 December 31, 2018 February 14, 2019 — 15.8 15.8 31.6 0.3015 March 31, 2019 May 15, 2019 0.2 16.4 16.3 32.9 0.3126 June 30, 2019 August 14, 2019 0.4 16.9 17.0 34.3 0.3237 September 30, 2019 November 14, 2019 0.7 17.6 17.6 35.9 0.3355 December 31, 2019 February 13, 2020 1.2 18.2 18.2 37.6 0.3475 March 31, 2020 May 14, 2020 1.2 18.2 18.2 37.6 0.3475 June 30, 2020 August 13, 2020 1.2 18.2 18.2 37.6 0.3475 September 30, 2020 November 12, 2020 1.2 18.2 18.2 37.6 0.3475 December 31, 2020 February 11, 2021 1.2 18.2 18.2 37.6 0.3475 * For the period subsequent to IPO Oct 30, 2017 – Dec 31, 2017, prorated from minimum quarterly distribution amount of $0.2625 / unit. ** Due to rounding, numbers presented for the general partner may not precisely reflect the absolute figures. Earnings in excess of distributions are allocated to the limited partners based on their respective percentage interests. Payments made to the Partnership’s unitholders are determined in relation to actual distributions declared and are not based on the net income allocations used in the calculation of net income per unit. In addition to the common and subordinated units, the Partnership also identified the incentive distribution rights ("IDRs") currently held by the general partner as a participating security and uses the two-class method when calculating the net income per unit that is based on the weighted-average number of common units outstanding during the period. When calculating basic earnings per unit under the two-class method for a master limited partnership, net income for the current reporting period is reduced by the amount of available cash that will be distributed to the general partner and limited partners for that reporting period. The following tables show the allocation of net income to arrive at net income per unit for the years ended December 31, 2020, 2019 and 2018: For the years ended December 31, 2020 2019 2018 Net income attributable to the Partnership $ 168.4 $ 167.9 $ 133.1 Less: Incentive distribution rights currently held by the general partner 4.8 2.5 — Limited partners' distribution declared on common units 72.8 69.1 59.4 Limited partners' distribution declared on subordinated units 72.8 69.1 59.4 Net income attributable to the Partnership in excess of distributions $ 18.0 $ 27.2 $ 14.3 For the year ended December 31, 2020 General Partner Limited Partners' Common Units Limited Partners' Subordinated Units Total Distributions declared $ 4.8 $ 72.8 $ 72.8 $ 150.4 Net income attributable to the Partnership in excess of distributions — 9.0 9.0 18.0 Net income attributable to the Partnership $ 4.8 $ 81.8 $ 81.8 $ 168.4 Weighted average units outstanding (in millions): Basic and Diluted 52.4 52.4 104.8 Net income per limited partner unit (in dollars): Basic and Diluted $ 1.56 $ 1.56 For the year ended December 31, 2019 General Partner Limited Partners' Common Units Limited Partners' Subordinated Units Total Distributions declared $ 2.5 $ 69.1 $ 69.1 $ 140.7 Net income attributable to the Partnership in excess of distributions — 13.6 13.6 27.2 Net income attributable to the Partnership $ 2.5 $ 82.7 $ 82.7 $ 167.9 Weighted average units outstanding (in millions): Basic and Diluted 52.4 52.4 104.8 Net income per limited partner unit (in dollars): Basic and Diluted $ 1.58 $ 1.58 Year Ended December 31, 2018 General Partner Limited Partners' Common Units Limited Partners' Subordinated Units Total Distributions declared $ — $ 59.4 $ 59.4 $ 118.8 Net income attributable to the Partnership in excess of distributions — 7.2 7.1 14.3 Net income attributable to the Partnership $ — $ 66.6 $ 66.5 $ 133.1 Weighted average units outstanding (in millions): Basic and Diluted 52.4 52.4 104.8 Net income per limited partner unit (in dollars): Basic and Diluted $ 1.27 $ 1.27

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The carrying amounts of accounts receivable, other current assets, accounts payable, and other current liabilities approximate their fair values due to their short-term nature. The carrying value of borrowings under the term loan as of December 31, 2020, and the credit facility as of December 31, 2019, approximate fair value as the interest rates are reflective of market rates.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Legal Proceedings The Partnership is a party to ongoing legal proceedings in the ordinary course of business. While the outcome of these proceedings cannot be predicted with certainty, we do not believe the results of these proceedings, individually or in the aggregate, will have a material adverse effect on our business, financial condition, results of operations or liquidity. In addition, pursuant to the terms of the various agreements under which we acquired assets from BP since the IPO, BP will indemnify us for certain liabilities relating to litigation and environmental matters attributable to the ownership or operation of the acquired assets prior to our acquisition of those assets. Indemnification Under our omnibus agreement, our Parent will indemnify us for certain environmental liabilities, litigation and other matters attributable to the ownership or operation of our assets prior to our ownership. For the purposes of determining the indemnified amount of any loss suffered or incurred by the Partnership, the Partnership’s ownership of 28.5% in Mars and 65% in Mardi Gras, and Mardi Gras’ 56% ownership in Caesar, 53% ownership in Cleopatra, 65% ownership in Endymion and 65% ownership in Proteus will be considered. Indemnification for certain identified environmental liabilities is subject to a cap of $25.0 million without any deductible. Other matters covered by the omnibus agreement are subject to a cap of $15.0 million and an aggregate deductible of $0.5 million before we are entitled to indemnification. Indemnification for any unknown environmental liabilities was limited to liabilities due to occurrences on or before October 30, 2017, which were identified prior to October 30, 2020. We continue to maintain indemnification by our general partner for matters previously discovered. To the extent that unknown environmental liabilities arise relating to prior ownership, the Partnership will be liable. The Interest Purchase Agreement contains customary representations, warranties and covenants of our Parent and the Partnership. Our Parent, on the one hand, and the Partnership, on the other hand, have agreed to indemnify each other and their respective affiliates, officers, directors and other representatives against certain losses, including those resulting from any breach of their representations, warranties or covenants contained in the Interest Purchase Agreement, subject to certain limitations and survival periods. This agreement covers the Partnership’s ownership of 22.7% in Ursa and 25% in KM Phoenix. Environmental Matters We are subject to federal, state, and local environmental laws and regulations. We record provisions for environmental liabilities based on management’s best estimates, using all information that is available at the time. In making environmental liability estimations, we consider the material effect of environmental compliance, pending legal actions against us and potential third-party liability claims. Often, as the remediation evaluation and effort progress, additional information is obtained, requiring revisions to estimated costs. We are indemnified by our Parent under the omnibus agreement against environmental cleanup costs for incidents that occurred prior to our ownership. Revisions to the estimated environmental liability for conditions that are not indemnified under the omnibus agreement with our Parent are reflected in our consolidated statements of operations in the year in which they are probable and reasonably estimable. We accrued $3.4 million and $3.7 million for environmental liabilities at December 31, 2020 and 2019, respectively. These balances are broken down on the consolidated balance sheets as follows: December 31, Balance sheet location 2020 2019 Current portion of environmental remediation obligations Other current liabilities $ 0.4 $ 0.6 Long-term portion of environmental remediation obligations Other liabilities 3.0 3.1 Total $ 3.4 $ 3.7 The balances are related to incidents that occurred prior to our ownership and are entirely indemnified by our Parent. As a result, we recorded corresponding indemnification assets of $3.4 million and $3.7 million on the consolidated balance sheet as of December 31, 2020, and 2019, respectively. These balances are broken down on the consolidated balance sheets as follows: December 31, Balance sheet location 2020 2019 Current portion of indemnification assets Other current assets $ 0.4 $ 0.6 Non-current portion of indemnification assets Other assets 3.0 3.1 Total $ 3.4 $ 3.7 Griffith Station Incident On June 13, 2019, a building fire occurred at the Griffith Station on BP2. Management performed an evaluation of the assets and determined that an impairment was required. A charge of $4.4 million for the impairment was recorded under "Impairment and other, net" on our consolidated statements of operations for the year ended December 31, 2019. In addition, we incurred $1.6 million as a response expense for the year ended December 31, 2019. Our assets are insured with a deductible of $1.0 million per incident. We accrued an offsetting insurance receivable of $5.0 million resulting in a net charge of $1.0 million to "Impairment and other, net" for the year ended December 31, 2019. The insurance receivable was recorded as $4.3 million under "Other current assets" and $0.7 million under "Other assets" on our consolidated balance sheet as of December 31, 2019. During the year ended December 31, 2020, we incurred $0.4 million for response expense and received $2.9 million of insurance proceeds. The proceeds have been recorded under "Proceeds from insurance claims" in our consolidated statements of cash flows for the year ended December 31, 2020, leaving a balance of $2.5 million recorded under "Other current assets" on our consolidated balance sheets as of December 31, 2020, for insurance proceeds expected to be received in 2021. In the event that insurance proceeds exceed the receivable balance, such amounts would be recognized as a gain. Commitments We hold easements or rights-of-way ("ROWs") arrangements from landowners permitting the use of land for the construction and operation of our pipeline systems. We incurred ROWs expenses, operating lease expenses and service contract expenses of $0.2 million for the years ended December 31, 2020, 2019 and 2018, respectively. Such amounts are included in Operating expenses – third parties on the consolidated statements of operations. These ROWs are not within the scope of ASC 842. At December 31, 2020, our future minimum commitment for contracts in excess of one year is as follows: Total 2021 2022 2023 2024 2025 Thereafter Rights-of-way $ 3.0 $ 0.1 $ 0.1 $ 0.1 $ 0.1 $ 0.1 $ 2.5 Total $ 3.0 $ 0.1 $ 0.1 $ 0.1 $ 0.1 $ 0.1 $ 2.5

Transactions with Major Custome

Transactions with Major Customers and Concentration of Credit Risk	12 Months Ended
	Dec. 31, 2020
Risks and Uncertainties [Abstract]
Transactions with Major Customers and Concentration of Credit Risk	Transactions with Major Customers and Concentration of Credit Risk Our Parent accounted for 97.8%, 97.7% and 97.6% of our total revenues for the years ended December 31, 2020, 2019 and 2018, respectively. We are potentially exposed to concentration of credit risk primarily through our accounts receivable from our Parent for the pipeline transportation services that we provide. These receivables have payment terms of 30 days or less. We have no history of collectability issues with our Parent. We have a concentration of trade receivables due from customers in the oil and gas industry, which may impact our overall exposure to credit risk as they may be similarly affected by changes in economic, regulatory and other factors. We manage our exposure to credit risk through credit analysis, credit limit approvals and monitoring procedures, and for certain transactions, we may request letters of credit, prepayments or guarantees. As of December 31, 2020 and 2019, there were no such arrangements. We have concentrated credit risk for cash by maintaining deposits with an affiliate of BP and a major bank. Amounts on deposit in the major bank may at times exceed amounts covered by insurance provided by the United States Federal Deposit Insurance Corporation ("FDIC"). We monitor the financial health of the affiliate and major bank and have not experienced any losses in such accounts and believe we are not exposed to any significant credit risk. At December 31, 2020 and 2019, we had $126.7 million and $98.6 million

Unit-Based Compensation

Unit-Based Compensation	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Unit-Based Compensation	Unit-Based Compensation Long-Term Incentive Plan On October 26, 2017, we adopted BP Midstream Partners LP 2017 Long Term Incentive Plan (the “LTIP”). Awards under the LTIP are available for eligible officers, directors, employees and consultants of the general partner and its affiliates, who perform services for the Partnership. The LTIP allows the Partnership to grant unit options, unit appreciation rights, restricted units, phantom units, unit awards, cash awards, performance awards, distribution equivalent rights, substitute awards and other unit-based awards. The maximum aggregate number of common units that may be issued pursuant to the awards granted under the LTIP shall not exceed 5,502,271, subject to proportionate adjustment in the event of unit splits and similar events. Unit-Based Awards under the LTIP Phantom units vest on the first anniversary of the date of grant. As a part of the phantom unit awards, the grantees will also receive distribution equivalent rights that entitle them, prior to vesting, with distributions for the same amounts that are distributed to the common unit holders. Distribution equivalent rights accrue in the form of either cash or additional phantom units. These phantom units do not convey voting rights. The following is a summary of phantom unit award activities of the Partnership’s common units from 2018 to 2020: Phantom Units Number of Units Weighted Average Grant Date Fair Value per Unit (in dollars) Aggregate Fair Value Outstanding at December 31, 2017 8,468 $ 17.48 Granted 3,737 20.07 $ 75 Vested (8,468) 17.48 Outstanding at December 31, 2018 3,737 20.07 Granted 15,227 16.64 $ 253 Vested (3,737) 20.07 Outstanding at December 31, 2019 15,227 16.64 Granted 16,038 14.03 $ 225 Vested (15,227) 16.64 Outstanding at December 31, 2020 16,038 $ 14.03 Total compensation expense recognized for phantom unit awards were $232 thousand, $239 thousand and $177 thousand for 2020, 2019 and 2018, respectively. These amounts are included in General and administrative – related parties on the consolidated statements of operations. The unrecognized compensation cost related to phantom unit awards was $34 thousand at December 31, 2020, which is expected to be recognized over a weighted average period of 0.2 years. There were no forfeitures in the years ended December 31, 2020, 2019 and 2018.

Variable Interest Entity

Variable Interest Entity	12 Months Ended
	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Variable Interest Entity	Variable Interest Entity Mardi Gras is a Delaware limited liability company and a pass-through entity for federal and state income tax purposes. Mardi Gras holds equity interests in the Mardi Gras Joint Ventures and accounts for them as equity method investments. Mardi Gras does not have any other operations or activities. The remaining interests in each of the Mardi Gras Joint Ventures are owned by unaffiliated third-party investors. Each of the Mardi Gras Joint Ventures is managed by their respective management committee, and decisions made by these management committees require approval of two or more members that are not affiliates with equity interest holdings meeting certain thresholds. On October 30, 2017, our Parent contributed to us 20% of its economic interest and 100% of its managing member interest in Mardi Gras. The remainder of the economic interest in Mardi Gras was held 79% by BP Pipelines and 1% by an affiliate of BP. Through our managing member interest in Mardi Gras, we have the right to vote 100% of Mardi Gras’ interest in each of the Mardi Gras Joint Ventures. We determined that Mardi Gras is a variable interest entity because (i) we hold disproportional voting rights as compared to our economic interest in Mardi Gras, and (ii) substantially all of Mardi Gras’ activities involve or are conducted on behalf of our Parent, which holds disproportionately few voting rights. On October 1, 2018, pursuant to the Interest Purchase Agreement we completed the acquisition of an additional 45% interest in Mardi Gras from BP Pipelines. This reduced the non-controlling interest on Mardi Gras from 80% to 35%. The managing member interest in Mardi Gras provides us with the unilateral power to direct the activities of Mardi Gras that most significantly impact its economic performance including the right to exercise the voting rights of BP for each of the Mardi Gras Joint Ventures. In addition, our obligations to absorb the expected losses of and the right to receive the residual returns from Mardi Gras relative to our economic ownership is significant to Mardi Gras. As a result, we are the primary beneficiary of Mardi Gras and consolidate Mardi Gras. We have the obligation to provide financial support to Mardi Gras if all members unanimously determine that additional capital contributions are necessary to fund Mardi Gras’ operations. The assets of Mardi Gras can only be used to satisfy its own obligations, which were zero at December 31, 2020 and 2019. Under the current limited liability company agreement of Mardi Gras, creditors of Mardi Gras, if any, do not have any recourse to the general credit of the Partnership. The financial position of Mardi Gras as of December 31, 2020 and 2019 and its financial performance and cash flows for each of the three years ended December 31, 2020, 2019 and 2018, as reflected in our consolidated financial statements, are as follows: As of December 31, 2020 2019 Balance sheet Equity method investments $ 378.5 $ 391.3 Non-controlling interests 132.5 136.9 December 31, 2020 2019 2018 Statement of operations Income from equity method investments $ 57.0 $ 54.8 $ 47.9 Less: Net income attributable to non-controlling interests 19.9 19.2 32.6 Net impact on Net income attributable to the Partnership $ 37.1 $ 35.6 $ 15.3 December 31, 2020 2019 2018 Statement of cash flows Cash flows from operating activities Distributions of earnings received from equity method investments $ 57.0 $ 54.8 $ 47.9 Cash flows from investing activities Distribution in excess of earnings from equity method investments 12.8 11.5 19.7 Cash flows from financing activities Distributions to non-controlling interests (24.3) (23.2) (46.4) Net change on BPMP's cash and cash equivalents $ 45.5 $ 43.1 $ 21.2

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation Consolidated financial statements have been prepared under the rules and regulations of the Securities and Exchange Commission (“SEC”). These rules and regulations conform to the accounting principles contained in the Financial Accounting
Principles of Consolidation	Principles of Consolidation Our consolidated financial statements include all subsidiaries, where the Partnership has control and a variable interest entity ("VIE") of which we are the primary beneficiary. The assets and liabilities in the consolidated financial statements have been reflected on a historical basis. All inter-company accounts and transactions are eliminated upon consolidation. We evaluate our ownership, contractual arrangements and other interests in entities to determine if these entities are VIEs and whether we are the primary beneficiary of the VIE. In determining whether we are the primary beneficiary of a VIE and therefore required to consolidate the VIE, we apply a qualitative approach that determines whether we have both (1) the power to direct the activities of the VIE that most significantly impact the economic performance and (2) the obligation to absorb the majority of losses of or the rights to receive the majority of the benefits from the VIE that could potentially be significant to the VIE. We continuously assess whether we are the primary beneficiary of a VIE as changes to existing relationships or future transactions may result in the consolidation or deconsolidation, as the case may be, of such VIE. We consolidate BP2, River Rouge and Diamondback, as we control these entities through 100% of the ownership interest. We control and consolidate Mardi Gras via an agreement between us and our Parent, under which we have the right to vote 100% of Mardi Gras' interests in each of the Mardi Gras Joint Ventures. We have determined that we are the primary beneficiary of Mardi Gras. Refer to Note 16 - Variable Interest Entity for further discussion.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported on the consolidated financial statements and disclosures included in the accompanying notes. Actual results could differ from these estimates.
Common Control Transactions	Common Control TransactionsAssets and businesses acquired from our Parent and its subsidiaries are accounted for as common control transactions whereby the net assets acquired are included in our consolidated balance sheets at their historical carrying value. If any recognized consideration transferred in such a transaction exceeds the historical carrying value of the net assets acquired, the excess is treated as a capital distribution to our Parent, similar to a dividend. If the historical carrying value of the net assets acquired exceeds any recognized consideration transferred including, if applicable, the fair value of any limited partner units issued, such excess is treated as a capital contribution from our Parent.
Revenue Recognition	Revenue Recognition We recognize revenue at an amount that reflects the consideration to which we expect to be entitled in exchange for transferring goods or services to a customer. We include certain disclosures regarding qualitative and quantitative information regarding the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. Refer to Note 4 - Revenue Recognition for further information.
Equity Method Investments	Equity Method Investments We account for an investment under the equity method if we have the ability to exercise significant influence, but not control, over the investee. Under the equity method of accounting, the investment is recorded at its initial carrying value on the consolidated balance sheets and is adjusted for capital contributions, dividends received and our share of the investee’s earnings or losses, which is recorded as a component of Income from equity method investments on the consolidated statements of operations. We evaluate equity method investments for impairment when events or changes in circumstances indicate, in our management’s judgment, that a decline in value is other than temporary. Factors that may indicate that a decline in value is
Property, plant and equipment	Property, plant and equipment Our property, plant and equipment is recorded at its historical cost of construction, or the carrying value of the transferring entity in a transaction under common control, or at fair value in a business combination. We record depreciation using the straight-line method with the following useful lives: Depreciable Land — ROW assets — Buildings and improvements 16 - 40 Pipelines and equipment 17 - 40 Other 4 - 23 Construction in progress — Upon the sale or retirement of property, plant and equipment, the cost and related accumulated depreciation are removed, and any resulting gain or loss is recorded on the consolidated statements of operations. Ordinary maintenance and repair costs are generally expensed as incurred. Such costs are recorded in Maintenance expenses- third parties and Maintenance expenses-related parties on our consolidated statements of operations. Costs of major renewals, betterments and replacements are capitalized as Property, plant and equipment. For constructed assets, we capitalize all construction-related direct labor and material costs, as well as indirect construction costs.
Impairment of Long-lived Assets	Impairment of Long-lived AssetsWe evaluate long-lived assets of identifiable business activities for impairment when events or changes in circumstances indicate, in our management’s judgment, that the carrying value of such assets may not be recoverable. These events include market declines that are believed to be other than temporary, changes in the manner in which we intend to use a long-lived asset, decisions to sell an asset and adverse changes in the legal or business environment, such as adverse actions by regulators. If an event occurs, which is a determination that involves judgment, we evaluate the recoverability of our carrying values of an asset group based on the long-lived assets’ ability to generate future cash flows on an undiscounted basis. If the carrying amount is higher than the undiscounted cash flows, we further evaluate the impairment loss by comparing management’s estimate of the fair value of the assets to the carrying value of such assets. We record a loss for the amount that the carrying value exceeds the estimated fair value.
Cash Equivalents	Cash Equivalents Cash equivalents are highly liquid, short-term investments that are readily convertible to known amounts of cash and will mature within 90 days or less from the date of acquisition. We record cash equivalents, if any, at its carrying value, which approximates its fair value.
Accounts Receivable and Allowance for Doubtful Accounts	Accounts Receivable and Allowance for Doubtful Accounts Accounts receivable represent valid claims against customers for services rendered, net of allowances for doubtful accounts. We assess the creditworthiness of our counterparties on an ongoing basis and require security, including prepayments and other forms of collateral, when appropriate. Our policy is to establish provisions for losses on accounts receivable due from shippers if we determine that we will not collect all or part of the outstanding balance.
Income Taxes	Income Taxes BP Midstream Partners LP is treated as a partnership for federal and state income tax purposes, with each partner being separately taxed on its share of taxable income. We are not subject to U.S. federal income taxes. Rather, our taxable income flows through to the owners, who are responsible for paying the applicable income taxes on the income allocated to them. For tax years beginning on or after January 1, 2018, we are subject to partnership audit rules enacted as part of the Bipartisan Budget Act of 2015 (the “Centralized Partnership Audit Regime”). Under the Centralized Partnership Audit Regime, any IRS audit of the Partnership would be conducted at the Partnership level, and if the IRS determines an adjustment, the default rule is that we would pay an “imputed underpayment” including interest and penalties, if applicable. We may instead elect to make a “push-out” election, in which case the partners for the year that is under audit would be required to take into account the adjustments on their own personal income tax returns. Our partnership agreement does not stipulate how we will address imputed underpayments. If we receive an imputed underpayment, a determination will be made based on the relevant facts and circumstances that exist at that time. We may treat any payments of imputed underpayment, which are made on behalf of our unitholders, as distribution of cash to such unitholders.
Asset Retirement Obligations	Asset Retirement Obligations Asset retirement obligations represent legal and constructive obligations associated with the retirement of long-lived assets that result from the acquisition, construction, development and/or normal use of the asset. We record liabilities for obligations related to the retirement and removal of long-lived assets used in our businesses at fair value on a discounted basis when they are incurred and can be reasonably estimated. Amounts recorded for the related assets are increased by the amount of these obligations. Over time, the liabilities increase due to the change in their present value, and the initial capitalized costs are depreciated over the useful lives of the related assets. The liabilities are eventually extinguished when settled at the time the asset is taken out of service. Although the Wholly Owned Assets will be replaced as needed, in management's judgement, the pipelines will continue to exist for an indefinite period of time. Therefore, there is uncertainty around the asset retirement settlement dates. As a result, we determined that there is not sufficient information to make a reasonable estimate of the asset retirement obligations for the Wholly Owned Assets, and we did not recognize any asset retirement obligations as of December 31, 2020 and 2019.
Legal	Legal We are subject to litigation and regulatory proceedings as the result of our business operations and transactions. We utilize both internal and external counsel in evaluating our potential exposure to adverse outcomes from orders, judgments or settlements. In general, we expense legal costs as incurred.
Environmental Matters	Environmental Matters We are subject to federal, state, and local environmental laws and regulations. These laws require us to take future action to remediate the effects on the environment of prior disposal or release of chemicals or petroleum substances by us or other parties. Environmental expenditures that are required to obtain future economic benefits from its assets are capitalized as part of those assets. Expenditures that relate to an existing condition caused by past operations and that do not contribute to current or future earnings shall be expensed, unless already provisioned for, which then shall be charged against provisions. Provisions are recognized when we have a present legal or constructive obligation as a result of a past event, if it is probable that an outflow of resources embodying economic benefits will be required to settle the obligation and a reliable estimate can be made of the amount of the obligation. We do not discount environmental liabilities, and we record environmental liabilities when environmental assessments and/or remedial efforts are probable, and when we can reasonably estimate the costs. In making environmental liability estimations, we consider the material effect of environmental compliance, pending legal actions against us and potential third-party liability claims. Often, as the remediation evaluation and effort progresses, additional information is obtained, requiring revisions to estimated costs. Generally, our recording of these provisions coincides with our commitment to a formal plan of action, or if earlier, on the closure or divestment of inactive sites. We recognize receivables for anticipated associated insurance recoveries when such recoveries are deemed to be probable. The ultimate requirement for remediation and its cost are inherently difficult to estimate. We believe that the outcome of these uncertainties should not have a material adverse effect on our financial condition, cash flows, or operating results. Our existing environmental conditions prior to the IPO are obligations contributed to us by the prior operator of these facilities, BP Pipelines, who has agreed to indemnify us with respect to such conditions under the terms of an omnibus agreement that we entered into in connection with the IPO. For provisions related to such conditions, we record indemnification assets in our consolidated balance sheets in the amounts that equal the provisions. Subsequent to the IPO, revisions to the estimated environmental liability for conditions that are not indemnified under the omnibus agreement with our Parent are reflected in our consolidated statements of operations when they are probable and reasonably estimable. For additional information regarding our environmental matters, refer to Note 13 - Commitments and Contingencies .
Other Contingencies	Other Contingencies We recognize liabilities for contingencies when we have an exposure that indicates it is both probable that a liability has been incurred and the amount of loss can be reasonably estimated. Where the most likely outcome of a contingency can be reasonably estimated, we accrue a liability for that amount. Where the most likely outcome cannot be estimated, a range of potential losses is established and if no one amount in that range is more likely than any other, the lower end of the range is accrued. To the extent that actual outcomes differ from our estimates, or additional facts and circumstances cause us to revise our estimates, our earnings will be affected.
Fair Value Estimates	Fair Value Estimates Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. We categorize assets and liabilities measured at fair value into one of three levels depending on the ability to observe inputs employed in their measurement: • Level 1 inputs are quoted prices in active markets for identical assets or liabilities. • Level 2 inputs are inputs that are observable, either directly or indirectly, other than quoted prices included within level 1 for the asset or liability. • Level 3 inputs are unobservable inputs for the asset or liability reflecting significant modifications to observable related market data or our assumptions about pricing by market participants.
Net Income per Unit	Net Income per UnitNet income per unit applicable to common limited partner units and to subordinated limited partner units is computed by dividing the respective limited partners’ interest in net income by the weighted average number of common units and subordinated units, respectively, outstanding for the period. Because we have more than one class of participating securities, we use the two-class method when calculating the net income per unit applicable to limited partners. The classes of participating securities include common units, subordinated units and incentive distribution rights.
Unit-Based Compensation	Unit-Based Compensation The fair value of phantom unit awards granted to non-employee directors is based on the fair market value of our common units on the date of grant. Our unit-based compensation expenses are recognized ratably over the vesting term of the awards. We have elected to recognize the impact of forfeitures only when they occur.
Leases	Leases We recognize an operating lease right-of-use (“ROU”) asset and a corresponding operating lease liability on our consolidated balance sheets based on the present value of the future minimum lease payments over the lease term at commencement date for arrangements with duration greater than one year. We use our incremental borrowing rate to determine the present value of future minimum lease payments over the duration of the lease term, which is determined to be reasonably certain. We do not separate lease and non-lease components for accounting purposes.
Revenue Recognition	Revenue Recognition We recognize revenue over time or at a point in time, depending on the nature of the performance obligations contained in the respective contract with customers. A performance obligation is our unit of account and it represents a promise in a contract to transfer goods or services to the customer. The contract transaction price, which is the amount of consideration to which an entity expects to be entitled in exchange for transferring promised goods or services to a customer, is allocated to each performance obligation and recognized as revenue when or as the performance obligation is satisfied. The following is an overview of our significant revenue stream, including a description of the respective performance obligations and related methods of revenue recognition. Pipeline Transportation Revenue from pipeline transportation is comprised of tariffs and fees associated with the transportation of liquid petroleum products, generally at published tariffs and in certain instances, revenue from MVC contracts at negotiated rates. Tariff revenue is recognized either at the point of delivery or at the point of receipt, pursuant to specifications outlined in the respective tariffs. We record revenue for crude oil, refined products and diluent transportation during the period in which they are earned (i.e., either physical delivery of product has taken place or the services designated in the contract have been performed). Partnership services are typically billed on a monthly basis, and we generally do not offer extended payment terms. We accrue revenue based on services rendered but not billed for that accounting month. Billings to BP Products for deficiency volumes under its MVCs, if any, are recorded as deferred revenue and credits, a contract liability, on the consolidated balance sheets, as BP Products has the right to make up the deficiency volumes within the measurement period specified by the agreements. Deferred revenue under these arrangements is recognized into revenue once it is deemed remote that the customer will meet its required annual MVC. If the customer does satisfy its MVC by shipping the deficiency volumes within the same calendar year, it may receive a refund of excess payments. We recognized $13.2 million, $5.6 million and $8.0 million of deficiency revenue under the throughput and deficiency agreements with BP Products for the years ended December 31, 2020, 2019 and 2018, respectively. Allowance Oil The tariff for crude oil transportation at BP2 includes a fixed loss allowance (“FLA”). An FLA factor per barrel, a fixed percentage, is a separate fee that is considered a part of the transaction price under the applicable crude oil tariff to cover evaporation and other losses in transit. The amount of revenue recognized is a product of the quantity transported, the applicable FLA factor and the settlement price during the month the product is transported. The settlement price for volumes accumulated is determined using a summation of the calendar-month average of West Texas Intermediate (“WTI”) on the New York Mercantile Exchange with pricing input from the month of movement, pursuant to a related party agreement that we entered into with our affiliate. The settlement price is fixed and determinable upon the completion of transportation. We settle the allowance oil at the end of each period. The balances are entirely recorded in Accounts receivable - related parties in the consolidated balance sheets.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Depreciable Lives	We record depreciation using the straight-line method with the following useful lives: Depreciable Land — ROW assets — Buildings and improvements 16 - 40 Pipelines and equipment 17 - 40 Other 4 - 23 Construction in progress —

Revenue Recognition (Tables)

Revenue Recognition (Tables)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	The following table provides information about disaggregated revenue: Year Ended December 31, Disaggregation of revenue 2020 2019 2018 Transportation services revenue - third parties 2.9 $ 3.0 $ 2.8 Transportation services revenue - related parties 126.0 125.5 113.6 Total revenue $ 128.9 $ 128.5 $ 116.4
Summary of Remaining Performance Obligation, Expected Timing of Satisfaction		The values in the table below represent the fixed portion of the MVC arrangements with our existing customer contracts, summarized as future performance obligations as of December 31, 2020. The unfulfilled performance obligations included in the table below are expected to be recognized in revenue in the specified periods: Unfulfilled performance obligations As of December 31, 2020 2021 $ 106.0 2022 102.2 2023 98.4 Total $ 306.6
Summary of Contract with Customer, Assets and Liabilities		The following table provides information about receivables from contracts with customers, contract assets and contract liabilities: As of December 31, Contract balances 2020 2019 Receivables from contracts with customers - third parties $ 0.2 $ 0.6 Receivables from contracts with customers - related parties 11.0 11.3 Deferred revenue and credits - related parties 1.8 1.5

Leases, Codification Topic 842

Leases, Codification Topic 842 (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Schedule of Future Minimum Lease Payments	The undiscounted future minimum lease payments and total lease liabilities as of December 31, 2020 are presented in the table below: (In thousands) December 31, 2020 2021 $ 64 2022 65 2023 66 2024 35 2025 36 Remaining years 443 Undiscounted future minimum lease payments 709 Less: Interest (180) Total lease liabilities $ 529

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Components of Property, Plant and Equipment	Property, plant and equipment consisted of the following: December 31, 2020 2019 Land $ 0.2 $ 0.2 Rights-of-way assets 1.4 1.4 Buildings and improvements 6.9 6.9 Pipelines and equipment 95.3 94.4 Other 0.8 0.5 Construction in progress 7.1 0.6 Property, plant and equipment 111.7 104.0 Less: Accumulated depreciation (43.8) (41.3) Property, plant and equipment, net $ 67.9 $ 62.7

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	12 Months Ended
	Dec. 31, 2020
Payables and Accruals [Abstract]
Schedule of Accrued Liabilities	liabilities consist of the following: December 31, 2020 2019 Accrued capital expenditures $ 4.1 $ 0.2 Accrued interest payable - related parties 0.9 4.2 Current portion of environmental remediation obligation 0.4 0.6 Current portion of lease liabilities 0.1 0.1 Accrued liabilities 2.3 1.5 Other current liabilities $ 7.8 $ 6.6

Related Party Transactions (Tab

Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2020
Related Party Transactions [Abstract]
Schedule of Related Party Transactions	During the years ended December 31, 2020, 2019 and 2018, we recorded the following amounts for related party expenses, which also included the expenses related to pension and retirement savings plans and share-based compensation discussed below: Years Ended December 31, 2020 2019 2018 Operating expenses—related parties $ 5.3 $ 5.8 $ 5.0 Maintenance expenses—related parties 0.4 0.3 0.1 General and administrative—related parties 14.5 14.1 14.1 Total operating, maintenance, and general corporate costs—related parties $ 20.2 $ 20.2 $ 19.2

Net Income Per Limited Partne_2

Net Income Per Limited Partner Unit (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Schedule of Earnings Per Share	For the years ended December 31, 2020 2019 2018 Net income attributable to the Partnership $ 168.4 $ 167.9 $ 133.1 Less: Incentive distribution rights currently held by the general partner 4.8 2.5 — Limited partners' distribution declared on common units 72.8 69.1 59.4 Limited partners' distribution declared on subordinated units 72.8 69.1 59.4 Net income attributable to the Partnership in excess of distributions $ 18.0 $ 27.2 $ 14.3 For the year ended December 31, 2020 General Partner Limited Partners' Common Units Limited Partners' Subordinated Units Total Distributions declared $ 4.8 $ 72.8 $ 72.8 $ 150.4 Net income attributable to the Partnership in excess of distributions — 9.0 9.0 18.0 Net income attributable to the Partnership $ 4.8 $ 81.8 $ 81.8 $ 168.4 Weighted average units outstanding (in millions): Basic and Diluted 52.4 52.4 104.8 Net income per limited partner unit (in dollars): Basic and Diluted $ 1.56 $ 1.56 For the year ended December 31, 2019 General Partner Limited Partners' Common Units Limited Partners' Subordinated Units Total Distributions declared $ 2.5 $ 69.1 $ 69.1 $ 140.7 Net income attributable to the Partnership in excess of distributions — 13.6 13.6 27.2 Net income attributable to the Partnership $ 2.5 $ 82.7 $ 82.7 $ 167.9 Weighted average units outstanding (in millions): Basic and Diluted 52.4 52.4 104.8 Net income per limited partner unit (in dollars): Basic and Diluted $ 1.58 $ 1.58

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Other Commitments	At December 31, 2020, our future minimum commitment for contracts in excess of one year is as follows: Total 2021 2022 2023 2024 2025 Thereafter Rights-of-way $ 3.0 $ 0.1 $ 0.1 $ 0.1 $ 0.1 $ 0.1 $ 2.5 Total $ 3.0 $ 0.1 $ 0.1 $ 0.1 $ 0.1 $ 0.1 $ 2.5

Unit-Based Compensation (Tables

Unit-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Phantom Units Activity	The following is a summary of phantom unit award activities of the Partnership’s common units from 2018 to 2020: Phantom Units Number of Units Weighted Average Grant Date Fair Value per Unit (in dollars) Aggregate Fair Value Outstanding at December 31, 2017 8,468 $ 17.48 Granted 3,737 20.07 $ 75 Vested (8,468) 17.48 Outstanding at December 31, 2018 3,737 20.07 Granted 15,227 16.64 $ 253 Vested (3,737) 20.07 Outstanding at December 31, 2019 15,227 16.64 Granted 16,038 14.03 $ 225 Vested (15,227) 16.64 Outstanding at December 31, 2020 16,038 $ 14.03

Variable Interest Entity (Table

Variable Interest Entity (Tables)	12 Months Ended
	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Variable Interest Entity	The financial position of Mardi Gras as of December 31, 2020 and 2019 and its financial performance and cash flows for each of the three years ended December 31, 2020, 2019 and 2018, as reflected in our consolidated financial statements, are as follows: As of December 31, 2020 2019 Balance sheet Equity method investments $ 378.5 $ 391.3 Non-controlling interests 132.5 136.9 December 31, 2020 2019 2018 Statement of operations Income from equity method investments $ 57.0 $ 54.8 $ 47.9 Less: Net income attributable to non-controlling interests 19.9 19.2 32.6 Net impact on Net income attributable to the Partnership $ 37.1 $ 35.6 $ 15.3 December 31, 2020 2019 2018 Statement of cash flows Cash flows from operating activities Distributions of earnings received from equity method investments $ 57.0 $ 54.8 $ 47.9 Cash flows from investing activities Distribution in excess of earnings from equity method investments 12.8 11.5 19.7 Cash flows from financing activities Distributions to non-controlling interests (24.3) (23.2) (46.4) Net change on BPMP's cash and cash equivalents $ 45.5 $ 43.1 $ 21.2

Business and Basis of Present_2

Business and Basis of Presentation (Details) - lease	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Oct. 01, 2018	Sep. 30, 2018
Variable Interest Entity [Line Items]
Number of reportable segments	1
Mars
Variable Interest Entity [Line Items]
Equity method investment, ownership percentage	28.50%	28.50%	28.50%
Mardi Gras
Variable Interest Entity [Line Items]
Equity method investment, ownership percentage	65.00%			65.00%	20.00%
Caesar
Variable Interest Entity [Line Items]
Equity method investment, ownership percentage	56.00%	56.00%	56.00%
Cleopatra
Variable Interest Entity [Line Items]
Equity method investment, ownership percentage	53.00%	53.00%	53.00%
Proteus
Variable Interest Entity [Line Items]
Equity method investment, ownership percentage	65.00%	65.00%	65.00%
Endymion
Variable Interest Entity [Line Items]
Equity method investment, ownership percentage	65.00%	65.00%	65.00%
Ursa
Variable Interest Entity [Line Items]
Equity method investment, ownership percentage	22.70%			22.70%
KM Phoenix
Variable Interest Entity [Line Items]
Equity method investment, ownership percentage	25.00%			25.00%	25.00%

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019	Oct. 01, 2018	Sep. 30, 2018
Variable Interest Entity [Line Items]
Allowance for doubtful accounts receivable	$ 0	$ 0
Asset retirement obligations	0	$ 0
Right-of-use assets	$ 513,000
BP Midstream Partners LP Predecessor
Variable Interest Entity [Line Items]
Subsidiary of limited partnership, ownership interest	100.00%
Mardi Gras
Variable Interest Entity [Line Items]
Managing member interest	100.00%
Mardi Gras
Variable Interest Entity [Line Items]
Equity method investment, ownership percentage	65.00%			65.00%	20.00%
Accounting Standards Update 2016-02
Variable Interest Entity [Line Items]
Operating lease, liability			$ 600,000

Summary of Significant Account

Summary of Significant Account Policies - Depreciable Lives (Details)	12 Months Ended
	Dec. 31, 2020
Buildings and improvements | Minimum
Property, Plant and Equipment [Line Items]
Depreciable Lives	16 years
Buildings and improvements | Maximum
Property, Plant and Equipment [Line Items]
Depreciable Lives	40 years
Pipelines and equipment | Minimum
Property, Plant and Equipment [Line Items]
Depreciable Lives	17 years
Pipelines and equipment | Maximum
Property, Plant and Equipment [Line Items]
Depreciable Lives	40 years
Other | Minimum
Property, Plant and Equipment [Line Items]
Depreciable Lives	4 years
Other | Maximum
Property, Plant and Equipment [Line Items]
Depreciable Lives	23 years

Acquisitions - Narrative (Detai

Acquisitions - Narrative (Details) - USD ($) $ in Thousands	Oct. 01, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2018
Class of Stock [Line Items]
Payments to acquire equity method investments	$ 468,000
Acquisition of non-controlling interest	380,800	$ 0	$ 0	$ 380,800
Acquisition of equity interests	$ 87,200	$ 0	$ 0	$ 87,200
Mars
Class of Stock [Line Items]
Equity method investment, ownership percentage		28.50%	28.50%	28.50%
Mardi Gras
Class of Stock [Line Items]
Equity method investment, additional ownership percentage purchased	45.00%
Equity method investment, ownership percentage	65.00%	65.00%			20.00%
Ursa
Class of Stock [Line Items]
Equity method investment, ownership percentage	22.70%	22.70%
KM Phoenix
Class of Stock [Line Items]
Equity method investment, ownership percentage	25.00%	25.00%			25.00%

Revenue Recognition Narrative (

Revenue Recognition Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Contract with customer, liability, revenue recognized	$ 13,200	$ 5,600	$ 8,000
Income related to fixed loss allowance	$ 5,800	$ 10,300	$ 8,800

Revenue Recognition Disaggregat

Revenue Recognition Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Third parties	$ 2,900	$ 3,000	$ 2,800
Related parties	126,000	125,500	113,600
Total revenue	128,900	128,500	116,400
Transportation services revenue - third parties
Disaggregation of Revenue [Line Items]
Third parties	2,900	3,000	2,800
Transportation services revenue - related parties
Disaggregation of Revenue [Line Items]
Related parties	$ 126,000	$ 125,500	$ 113,600

Revenue Recognition Future Perf

Revenue Recognition Future Performance Obligations (Details) $ in Thousands	Dec. 31, 2020USD ($)
Revenue from Contract with Customer [Abstract]
Remaining performance obligation	$ 306,600
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue from Contract with Customer [Abstract]
Remaining performance obligation	$ 106,000
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue from Contract with Customer [Abstract]
Remaining performance obligation	$ 102,200
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue from Contract with Customer [Abstract]
Remaining performance obligation	$ 98,400
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected timing of satisfaction	1 year

Revenue Recognition Contract Ba

Revenue Recognition Contract Balances (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables from contracts with customers	$ 200	$ 600
Transportation services revenue - related parties
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables from contracts with customers	11,000	11,300
Deferred revenue and credits - related parties	1,800	1,500
Transportation services revenue - third parties
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables from contracts with customers	$ 200	$ 600

Leases, Codification Topic 84_2

Leases, Codification Topic 842 (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)lease	Dec. 31, 2019USD ($)
Lessee, Lease, Description [Line Items]
Number of Operating Leases | lease	4
Operating Lease, Liability, Current	$ 100	$ 100
Right-of-use assets	513
Operating Lease, Liability, Noncurrent	$ 467
Lessee, Operating Lease, Annual Escalation, Percentage	3.00%
Operating Lease, Weighted Average Discount Rate, Percent	4.00%
Lessee, Operating Lease, Liability, Payments, Due	$ 709
Lessee, Operating Lease, Liability, Payments, Due Year Two	64
Lessee, Operating Lease, Liability, Payments, Due Year Three	65
Lessee, Operating Lease, Liability, Payments, Due Year Four	66
Lessee, Operating Lease, Liability, Payments, Due Year Five	35
Lessee, Operating Lease, Liability, Payments, Due after Year Five	$ 443
Schedule of Leases Statement of Financial Position	Amounts recognized in the accompanying consolidated balance sheets are as follows: Lease activity (in thousands) Balance sheet location December 31, 2020 December 31, 2019 ROU assets Other assets $ 513 $ 469 Current lease liability Other current liabilities $ 62 $ 60 Long-term lease liability Other liabilities $ 467 $ 417
Lessee, Operating Lease, Expiring in 2020 [Member]
Lessee, Lease, Description [Line Items]
Number of Operating Leases | lease	2
Lessee, Operating Lease, Expiring in 2036 [Member]
Lessee, Lease, Description [Line Items]
Number of Operating Leases | lease	2
Lessee, Operating Lease, Right of Renewal and Annual Escalation [Member]
Lessee, Lease, Description [Line Items]
Number of Operating Leases | lease	2
Lessee, Operating Lease, Non-Lease Component For Maintenance Expense [Member]
Lessee, Lease, Description [Line Items]
Number of Operating Leases | lease	2

Equity Method Investments - Nar

Equity Method Investments - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity Method Investments and Joint Ventures [Abstract]
Equity method investment, impairment loss	$ 0	$ 0	$ 0

Equity Method Investments - Sch

Equity Method Investments - Schedule of Equity Method Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Oct. 01, 2018	Sep. 30, 2018
Equity Method Investment, Financial Statement, Reported Amounts [Abstract]
Prior Period Reclassification Adjustment			$ 2,800
Proceeds From Equity Method Investment, Dividends Or Distributions, Return On Capital And Return Of Capital	$ 125,300	$ 131,400	117,800
Income from EMI	110,800	116,700	94,400
Carrying value	519,900	534,400	549,000
Equity Method Investments Revenues	538,600	560,500	470,800
Equity Method Investments Cost Of Revenue	250,200	246,000	200,900
Equity Method Investments Gross Profit	288,900	317,200	$ 270,400
Current assets	110,800	128,700
Equity Method Investments Assets Noncurrent	1,726,400	1,630,700
Equity Method Investments Liabilities Current	56,500	49,600
Equity Method Investments Liabilities Noncurrent	589,400	493,000
Equity Method Investments Members Equity	$ 1,191,300	$ 1,216,800
Mars
Equity Method Investment, Financial Statement, Reported Amounts [Abstract]
Percentage ownership	28.50%	28.50%	28.50%
Prior Period Reclassification Adjustment			$ 2,800
Proceeds From Equity Method Investment, Dividends Or Distributions, Return On Capital And Return Of Capital	$ 49,100	$ 53,400	47,500
Income from EMI	46,300	51,100	43,900
Carrying value	$ 54,100	$ 56,900	$ 59,100
Caesar
Equity Method Investment, Financial Statement, Reported Amounts [Abstract]
Percentage ownership	56.00%	56.00%	56.00%
Proceeds From Equity Method Investment, Dividends Or Distributions, Return On Capital And Return Of Capital	$ 16,100	$ 19,500	$ 21,000
Income from EMI	15,200	17,500	16,800
Carrying value	$ 116,500	$ 117,400	$ 119,400
Cleopatra
Equity Method Investment, Financial Statement, Reported Amounts [Abstract]
Percentage ownership	53.00%	53.00%	53.00%
Proceeds From Equity Method Investment, Dividends Or Distributions, Return On Capital And Return Of Capital	$ 8,900	$ 11,000	$ 10,500
Income from EMI	5,600	9,000	6,500
Carrying value	$ 114,300	$ 117,600	$ 119,600
Proteus
Equity Method Investment, Financial Statement, Reported Amounts [Abstract]
Percentage ownership	65.00%	65.00%	65.00%
Proceeds From Equity Method Investment, Dividends Or Distributions, Return On Capital And Return Of Capital	$ 20,500	$ 19,000	$ 18,100
Income from EMI	13,600	13,000	12,300
Carrying value	$ 68,400	$ 75,300	$ 81,300
Endymion
Equity Method Investment, Financial Statement, Reported Amounts [Abstract]
Percentage ownership	65.00%	65.00%	65.00%
Proceeds From Equity Method Investment, Dividends Or Distributions, Return On Capital And Return Of Capital	$ 24,300	$ 16,800	$ 18,000
Income from EMI	22,600	15,300	12,300
Carrying value	79,300	81,000	82,500
Others
Equity Method Investment, Financial Statement, Reported Amounts [Abstract]
Proceeds From Equity Method Investment, Dividends Or Distributions, Return On Capital And Return Of Capital	6,400	11,700	2,700
Income from EMI	7,500	10,800	2,600
Carrying value	$ 87,300	$ 86,200	$ 87,100
Total Mardi Gras Joint Ventures
Equity Method Investment, Financial Statement, Reported Amounts [Abstract]
Percentage ownership	65.00%			65.00%	20.00%
Ursa
Equity Method Investment, Financial Statement, Reported Amounts [Abstract]
Percentage ownership	22.70%			22.70%
KM Phoenix
Equity Method Investment, Financial Statement, Reported Amounts [Abstract]
Percentage ownership	25.00%			25.00%	25.00%

Property, Plant and Equipment_2

Property, Plant and Equipment (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 111,700,000	$ 104,000,000
Less: Accumulated depreciation	(43,800,000)	(41,300,000)
Property, plant and equipment, net	67,900,000	62,700,000
Impairment and other, net	0	1,000,000	$ 0
Impairment of Long-Lived Assets Held-for-use	4,400,000	0
Equity method investment, impairment loss	0	0	$ 0
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	200,000	200,000
Rights-of-way assets
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,400,000	1,400,000
Building and improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	6,900,000	6,900,000
Pipeline and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	95,300,000	94,400,000
Other
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	800,000	500,000
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 7,100,000	$ 600,000

Accrued Liabilities - Schedule

Accrued Liabilities - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accrued Environmental Loss Contingencies, Current	$ 400	$ 600
Operating Lease, Liability, Current	100	100
Current portion of lease liabilities	900	4,200
Other Accrued Liabilities, Current	2,300	1,500
Other current liabilities	7,800	6,600
Other Liabilities, Current	7,800	6,600
Accrued Liabilities	$ 4,100	$ 200

Debt (Details)

Debt (Details)	Oct. 30, 2017USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Feb. 24, 2020USD ($)	Oct. 01, 2018USD ($)
Debt Instrument [Line Items]
Line of credit facility maximum borrowing capacity	$ 600,000,000
Indebtedness threshold	$ 75,000,000
Weighted average interest rate		3.25%
Commitment fee percentage		0.10%
Utilization fee percentage		0.20%
Proceeds from issuance of debt – related parties		$ 468,000,000	$ 0	$ 468,000,000
Interest and fees incurred		8,300,000	16,500,000	$ 4,800,000
Outstanding borrowing		468,000,000	468,000,000
Long-term debt outstanding		$ 468,000,000	$ 468,000,000		$ 468,000,000	$ 468,000,000
London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate	0.85%
Maximum
Debt Instrument [Line Items]
Required consolidated leverage ratio	5
Required consolidated leverage ratio, potential temporary increase	5.5
Debt to EBITDA ratio, approval of related holding company	4.5

Related Party Transactions - Na

Related Party Transactions - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Oct. 01, 2018
Related Party Transaction [Line Items]
Revenue from related parties		$ 126,000	$ 125,500	$ 113,600
Accounts payable – related parties		1,900	1,700
Deferred revenues and credits – related parties		1,800	1,500
BP Products
Related Party Transaction [Line Items]
Revenue from related parties		13,200	5,600	$ 8,000
Deferred revenues and credits – related parties			1,500
BP Pipelines
Related Party Transaction [Line Items]
Annual fee paid to related party	$ 15,500	$ 13,600	$ 13,300
Parent
Related Party Transaction [Line Items]
Performance period		3 years
Mardi Gras
Related Party Transaction [Line Items]
Noncontrolling interest, ownership percentage by Parent		35.00%			80.00%

Related Party Transactions - Sc

Related Party Transactions - Schedule of Related Party Transactions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Operating expenses—related parties	$ 5,300	$ 5,800	$ 5,000
Maintenance expenses—related parties	400	300	100
General and administrative—related parties	14,500	14,100	14,100
Total operating, maintenance, and general corporate costs—related parties	20,200	$ 20,200	$ 19,200
Contractual Obligation	3,000
Contractual Obligation, Due in Next Fiscal Year	100
Contractual Obligation, Due after Fifth Year	2,500
Contractual Obligation, Due in Third Year	100
Contractual Obligation, Due in Fourth Year	100
Contractual Obligation, Due in Fifth Year	100
Contractual Obligation, Due in Second Year	100
Right of Ways Member
Related Party Transaction [Line Items]
Contractual Obligation	3,000
Contractual Obligation, Due in Next Fiscal Year	100
Contractual Obligation, Due after Fifth Year	2,500
Contractual Obligation, Due in Third Year	100
Contractual Obligation, Due in Fourth Year	100
Contractual Obligation, Due in Fifth Year	100
Contractual Obligation, Due in Second Year	$ 100

Net Income Per Limited Partne_3

Net Income Per Limited Partner Unit - Schedule of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	Nov. 12, 2020	Aug. 13, 2020	May 14, 2020	Feb. 13, 2020	Nov. 14, 2019	Aug. 14, 2019	May 15, 2019	Feb. 14, 2019	Nov. 15, 2018	Aug. 15, 2018	May 15, 2018	Feb. 15, 2018	Dec. 31, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income attributable to the Partnership													$ 133,100	$ 168,400	$ 167,900	$ 133,100
Partner distributions declared	$ 37,600	$ 37,600	$ 37,600	$ 37,600	$ 35,900	$ 34,300	$ 32,900	$ 31,600	$ 30,600	$ 28,600	$ 28,000	$ 18,700		150,400	140,700	118,800
Net income attributable to the Partnership in excess of distributions														$ 18,000	$ 27,200	$ 14,300
Weighted average units outstanding:
Basic (in shares)														104.8	104.8	104.8
Incentive distribution rights currently held by the General Partner
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income attributable to the Partnership														$ 4,800	$ 2,500	$ 0
Partner distributions declared	1,200	1,200	1,200	1,200	700	400	200	0	0	0	0	0		4,800	2,500	0
Net income attributable to the Partnership in excess of distributions														0	0	0
Limited partners' distribution declared on common units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income attributable to the Partnership														81,800	82,700	66,600
Partner distributions declared														72,800	69,100	59,400
Net income attributable to the Partnership in excess of distributions														$ 9,000	$ 13,600	$ 7,200
Weighted average units outstanding:
Basic (in shares)														52.4	52.4	52.4
Net income per limited partner unit (in dollars):
Basic (in dollars per share)														$ 1.56	$ 1.58	$ 1.27
Limited partners' distribution declared on subordinated units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income attributable to the Partnership														$ 81,800	$ 82,700	$ 66,500
Partner distributions declared	$ 18,200	$ 18,200	$ 18,200	$ 18,200	$ 17,600	$ 17,000	$ 16,300	$ 15,800	$ 15,300	$ 14,300	$ 14,000	$ 9,300		72,800	69,100	59,400
Net income attributable to the Partnership in excess of distributions														$ 9,000	$ 13,600	$ 7,100
Weighted average units outstanding:
Basic (in shares)														52.4	52.4	52.4
Net income per limited partner unit (in dollars):
Basic (in dollars per share)														$ 1.56	$ 1.58	$ 1.27

Net Income Per Limited Partne_4

Net Income Per Limited Partner Unit - Narrative (Details) - $ / shares	Nov. 12, 2020	Aug. 13, 2020	May 14, 2020	Feb. 13, 2020	Nov. 14, 2019	Aug. 14, 2019	May 15, 2019	Feb. 14, 2019	Nov. 15, 2018	Aug. 15, 2018	May 15, 2018	Feb. 15, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dividends per share (in dollars per share)	$ 0.3475	$ 0.3475	$ 0.3475	$ 0.3475	$ 0.3355	$ 0.3237	$ 0.3126	$ 0.3015	$ 0.2915	$ 0.2725	$ 0.2675	$ 0.1798

Net Income Per Limited Partne_5

Net Income Per Limited Partner Unit - Schedule of Distributions (Details) - USD ($) $ / shares in Units, $ in Thousands	Nov. 12, 2020	Aug. 13, 2020	May 14, 2020	Feb. 13, 2020	Nov. 14, 2019	Aug. 14, 2019	May 15, 2019	Feb. 14, 2019	Nov. 15, 2018	Aug. 15, 2018	May 15, 2018	Feb. 15, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Distribution Made to Limited Partner [Line Items]
Partner distributions declared	$ 37,600	$ 37,600	$ 37,600	$ 37,600	$ 35,900	$ 34,300	$ 32,900	$ 31,600	$ 30,600	$ 28,600	$ 28,000	$ 18,700	$ 150,400	$ 140,700	$ 118,800
Dividends per share (in dollars per share)	$ 0.3475	$ 0.3475	$ 0.3475	$ 0.3475	$ 0.3355	$ 0.3237	$ 0.3126	$ 0.3015	$ 0.2915	$ 0.2725	$ 0.2675	$ 0.1798
General Partner
Distribution Made to Limited Partner [Line Items]
Partner distributions declared	$ 1,200	$ 1,200	$ 1,200	$ 1,200	$ 700	$ 400	$ 200	$ 0	$ 0	$ 0	$ 0	$ 0	4,800	2,500	0
Limited Partner Common Units Member [Member]
Distribution Made to Limited Partner [Line Items]
Partner distributions declared	18,200	18,200	18,200	18,200	17,600	16,900	16,400	15,800	15,300	14,300	14,000	9,400
Limited Partners Subordinated Units
Distribution Made to Limited Partner [Line Items]
Partner distributions declared	$ 18,200	$ 18,200	$ 18,200	$ 18,200	$ 17,600	$ 17,000	$ 16,300	$ 15,800	$ 15,300	$ 14,300	$ 14,000	$ 9,300	$ 72,800	$ 69,100	$ 59,400

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Oct. 01, 2018	Sep. 30, 2018
Site Contingency [Line Items]
Environmental liability indemnification cap	$ 25,000
Other matters indemnification cap	15,000
Accrual for environmental loss contingencies	3,400	$ 3,700
Operating lease expense	200
Indemnification Asset For Environmental Loss Contingencies Current	400	600
Indemnification Asset For Environmental Loss Contingencies Noncurrent	3,000	3,100
Indemnification Asset For Environmental Loss Contingencies	3,400	3,700
Accrued Environmental Loss Contingencies, Current	400	600
Long-term portion of environmental remediation obligations	$ 3,000	$ 3,100
Mars
Site Contingency [Line Items]
Equity method investment, ownership percentage	28.50%	28.50%	28.50%
Mardi Gras
Site Contingency [Line Items]
Equity method investment, ownership percentage	65.00%			65.00%	20.00%
Caesar
Site Contingency [Line Items]
Equity method investment, ownership percentage	56.00%	56.00%	56.00%
Cleopatra
Site Contingency [Line Items]
Equity method investment, ownership percentage	53.00%	53.00%	53.00%
Endymion
Site Contingency [Line Items]
Equity method investment, ownership percentage	65.00%	65.00%	65.00%
Proteus
Site Contingency [Line Items]
Equity method investment, ownership percentage	65.00%	65.00%	65.00%
Ursa
Site Contingency [Line Items]
Equity method investment, ownership percentage	22.70%			22.70%
KM Phoenix
Site Contingency [Line Items]
Equity method investment, ownership percentage	25.00%			25.00%	25.00%
Omnibus Agreement
Site Contingency [Line Items]
Aggregate deductible	$ 500

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2020USD ($)
Site Contingency [Line Items]
Contractual Obligation	$ 3,000
Contractual Obligation, Due in Next Fiscal Year	100
Contractual Obligation, Due after Fifth Year	$ 2,500

Transactions with Major Custo_2

Transactions with Major Customers and Concentration of Credit Risk (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Concentration Risk [Line Items]
Cash and cash equivalents in excess of FDIC limits	$ 126,700	$ 98,600
BP Products | Sales Revenue, Net | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk	97.80%	97.70%	97.60%

Unit-Based Compensation - Narra

Unit-Based Compensation - Narrative (Details) - USD ($) $ in Thousands	2 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Phantom units granted, aggregate amount		$ 225	$ 253	$ 75
Phantom Share Units (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Phantom units granted (in shares)	3,737	16,038	15,227
Share-based compensation		$ 232	$ 239	$ 177
Unrecognized compensation cost related to phantom unit awards		$ 34
Weighted average recognition period		2 months 12 days
Forfeited (in shares)		0
Phantom Share Units (PSUs) | BP Midstream Partners LP 2017 Long Term Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum aggregate number of common units that may be issued (in shares)		5,502,271

Unit-Based Compensation - Phant

Unit-Based Compensation - Phantom Units Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	2 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Weighted Average Grant Date Fair Value per Unit (in dollars)
Phantom units granted, aggregate amount		$ 225	$ 253	$ 75
Phantom Share Units (PSUs)
Number of Units
Beginning balance outstanding (shares)		15,227	3,737
Granted (in shares)	3,737	16,038	15,227
Vested (in shares)		(15,227)	(3,737)	(8,468)
Ending balance outstanding (shares)		16,038	15,227
Weighted Average Grant Date Fair Value per Unit (in dollars)
Beginning balance outstanding (in dollars per share)		$ 16.64	$ 20.07
Granted (in dollars per share)	$ 20.07	14.03	16.64
Vested (in dollars per share)		16.64	20.07	$ 17.48
Ending balance outstanding (in dollars per share)		$ 14.03	$ 16.64

Variable Interest Entity - Narr

Variable Interest Entity - Narrative (Details) - USD ($)	Oct. 01, 2018	Oct. 30, 2017	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Variable Interest Entity, Primary Beneficiary | Mardi Gras
Variable Interest Entity [Line Items]
Assets of Mardi Gras			$ 0		$ 0
Mardi Gras
Variable Interest Entity [Line Items]
Managing member interest			100.00%
Non-controlling interest, ownership percentage	35.00%			80.00%
Mardi Gras | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Variable interest entity, ownership interest		20.00%
Managing member interest		100.00%
Subsidiary of limited partnership, parent ownership interest		79.00%
Subsidiary of limited partnership, affiliate other than parent interest		1.00%
Mardi Gras
Variable Interest Entity [Line Items]
Equity method investment, additional ownership percentage purchased	45.00%

Variable Interest Entity - Sche

Variable Interest Entity - Schedule of Variable Interest Entity (Details) - USD ($) $ in Thousands	2 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Balance sheet
Equity method investments (Note 6)		$ 519,900	$ 534,400	$ 549,000
Non-controlling interests		132,500	136,900
Statement of operations
Income from equity method investments		110,800	116,700	94,400
Less: Net income attributable to noncontrolling interests		19,900	19,200	32,600
Net income attributable to the Partnership	$ 133,100	168,400	167,900	133,100
Cash flows from operating activities
Distributions of earnings received from equity method investments		112,300	119,900	98,100
Cash flows from financing activities
Distributions to noncontrolling interests		(24,300)	(23,200)	(46,400)
Net cash used in financing activities		(174,700)	(157,900)	(80,300)
Net change in cash and cash equivalents		28,100	41,800	24,300
Variable Interest Entity, Primary Beneficiary | Mardi Gras
Balance sheet
Equity method investments (Note 6)		378,500	391,300
Statement of operations
Income from equity method investments		57,000	54,800	47,900
Net income attributable to the Partnership		37,100	35,600	15,300
Cash flows from operating activities
Distributions of earnings received from equity method investments		57,000	54,800	47,900
Cash flows from investing activities
Distribution in excess of earnings from equity method investments		12,800	11,500	19,700
Cash flows from financing activities
Net change in cash and cash equivalents		$ 45,500	$ 43,100	$ 21,200

Subsequent Events (Details)

Subsequent Events (Details) - USD ($)	Feb. 13, 2020	Dec. 31, 2020	Feb. 24, 2020	Dec. 31, 2019	Oct. 01, 2018	Oct. 30, 2017
Subsequent Event [Line Items]
Long-term debt outstanding		$ 468,000,000	$ 468,000,000	$ 468,000,000	$ 468,000,000
Line of credit facility maximum borrowing capacity						$ 600,000,000
Subsequent Event
Subsequent Event [Line Items]
Dividends per share (in dollars per share)	$ 0.3475
Total distribution paid	$ 37,600,000
Dividends paid to non-affiliated common unitholders	16,600,000
Net transfers to Parent	21,000,000
Incentive Distribution, Distribution	$ 1,200,000

Uncategorized Items - bpmp-2020

Label	Element	Value
Phantom Share Units (PSUs) [Member]
Share-Based Compensation Arrangement By Share-Based Payment Award, Equity Instruments Other Than Options, Outstanding, Weighted Average Grant Date Fair Value	bpmp_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageGrantDateFairValue	$ 17.48
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber	8,468