Oasis Midstream Partners (OMP) 10-K 28 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information Document - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 26, 2018	Jun. 30, 2017
Document Information [Line Items]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	OMP
Entity Registrant Name	Oasis Midstream Partners LP
Entity Central Index Key	1,652,133
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Public Float			$ 0
Common Units [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		13,761,766
Subordinated Units [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		13,750,000

Consolidated Balance Sheet

Consolidated Balance Sheet - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 883	$ 0
Accounts receivable	834	667
Accounts receivable from Oasis Petroleum	85,818	11,721
Insurance receivable	0	5,096
Prepaid expenses	778	1,006
Total current assets	88,313	18,490
Property, plant and equipment	653,928	453,695
Less: accumulated depreciation and amortization	(34,348)	(22,160)
Total property, plant and equipment, net	619,580	431,535
Other assets	2,013	3
Total assets	709,906	450,028
Current liabilities
Accounts payable	0	3,314
Accounts payable due to Oasis Petroleum	11,638	0
Accrued liabilities	58,818	32,179
Accrued interest payable	114	0
Current income taxes payable	0	41,063
Total current liabilities	70,570	76,556
Long-term debt	78,000	0
Deferred income taxes	0	40,084
Asset retirement obligations	1,316	1,713
Total liabilities	149,886	118,353
Commitments and contingencies
Net parent investment / partners’ capital
Net parent investment		331,675
Non-controlling interests	313,446
Total net parent investment / partners' capital	560,020
Total liabilities and net parent investment / partners' capital	709,906	$ 450,028
Public [Member] | Common Units [Member]
Net parent investment / partners’ capital
Partners' capital, units	137,888
Oasis [Member] | Common Units [Member]
Net parent investment / partners’ capital
Partners' capital, units	29,513
Oasis [Member] | Subordinated Units [Member]
Net parent investment / partners’ capital
Partners' capital, units	$ 79,173

Consolidated Balance Sheet Pare

Consolidated Balance Sheet Parenthetical	Dec. 31, 2017shares
Public [Member] | Common Units [Member]
Units outstanding (shares)	8,636,766
Unitholders [Member] | Common Units [Member]
Units outstanding (shares)	5,125,000
Unitholders [Member] | Subordinated Units [Member]
Units outstanding (shares)	13,750,000

Consolidated Statement of Opera

Consolidated Statement of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Total revenues		$ 182,216	$ 120,852	$ 104,696
Operating expenses
Direct operating		45,526	29,275	28,548
Depreciation and amortization		15,730	8,525	5,765
Impairment		0	0	2,073
General and administrative		18,597	12,112	10,215
Total operating expenses		79,853	49,912	46,601
Operating income		102,363	70,940	58,095
Interest expense, net of capitalized interest		(6,965)	(5,481)	(4,514)
Other income (expense)		7	(474)	(800)
Total other income (expense)		(6,958)	(5,955)	(5,314)
Income before income taxes		95,405	64,985	52,781
Income tax expense		(22,858)	(24,857)	(20,339)
Net income	$ 34,970	72,547	40,128	32,442
Less: Net income attributable to non-controlling interests subsequent to the initial public offering	23,332
Net income attributable to Oasis Midstream Partners LP	$ 11,638	$ 11,638
Common Units [Member]
Weighted average number of limited partner units outstanding - Basic
Weighted average number of limited partner units outstanding (Basic) (shares)		13,566
Weighted average number of limited partner units outstanding (Diluted) (shares)		13,568
Subordinated Units [Member]
Weighted average number of limited partner units outstanding - Basic
Weighted average number of limited partner units outstanding (Basic) (shares)		13,750
Weighted average number of limited partner units outstanding (Diluted) (shares)		13,750
Oasis Petroleum [Member]
Revenues
Midstream services		$ 179,849	120,258	104,675
Third Parties [Member]
Revenues
Midstream services		$ 2,367	$ 594	$ 21

Consolidated Statements of Chan

Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Noncontrolling Interest [Member]	Common Units [Member]	Public [Member]Common Units [Member]	Oasis [Member]Common Units [Member]	Oasis [Member]Subordinated Units [Member]
Increase (Decrease) in Partners' Capital [Roll Forward]
Beginning balance | Predecessor [Member]	$ 105,633
Beginning balance	105,633
Capital contributions prior to the initial public offering | Predecessor [Member]	66,091
Capital contributions prior to the initial public offering	66,091
Stock-based compensation | Predecessor [Member]	690
Stock-based compensation	690
Net income | Predecessor [Member]	32,442
Net income	32,442
Beginning balance | Predecessor [Member]	204,856
Beginning balance	204,856
Capital contributions prior to the initial public offering | Predecessor [Member]	85,780
Capital contributions prior to the initial public offering	85,780
Stock-based compensation | Predecessor [Member]	911
Stock-based compensation	911
Net income | Predecessor [Member]	40,128
Net income	40,128
Beginning balance | Predecessor [Member]	331,675
Beginning balance	331,675
Cumulative-effect adjustment for adoption of ASU 2016-09 | Predecessor [Member]	(59)
Cumulative-effect adjustment for adoption of ASU 2016-09	(59)
Capital contributions prior to the initial public offering | Predecessor [Member]	65,145
Capital contributions prior to the initial public offering	65,145
Stock-based compensation | Predecessor [Member]	999
Stock-based compensation	999
Net income | Predecessor [Member]	37,577
Net income	37,577
Ending balance (Predecessor [Member]) at Sep. 25, 2017	435,337
Ending balance at Sep. 25, 2017	435,337	$ 0		$ 0	$ 0	$ 0
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income	72,547
Ending balance (Predecessor [Member]) at Dec. 31, 2017	0
Ending balance at Dec. 31, 2017	560,020	313,446		137,888	29,513	79,173
Beginning balance (Predecessor [Member]) at Sep. 25, 2017	435,337
Beginning balance at Sep. 25, 2017	435,337	0		0	0	0
Increase (Decrease) in Partners' Capital [Roll Forward]
Elimination of current and deferred tax liabilities | Predecessor [Member]	104,005
Elimination of current and deferred tax liabilities	104,005
Net assets excluded from the initial public offering | Predecessor [Member]	(50,726)
Net assets excluded from the initial public offering	(50,726)
Allocation of net investment to unitholders | Predecessor [Member]	(488,616)
Allocation of net investment to unitholders	0	290,835			53,704	144,077
Net proceeds from the initial public offering			$ 134,185	134,185
Proceeds from the initial public offering distributed to Oasis Petroleum		(35,000)			(26,360)	(70,723)
Capital contributions from non-controlling interests	34,279	34,279
Stock-based compensation	53			53
Net income	34,970	23,332		3,650	2,169	5,819
Ending balance (Predecessor [Member]) at Dec. 31, 2017	0
Ending balance at Dec. 31, 2017	$ 560,020	$ 313,446		$ 137,888	$ 29,513	$ 79,173

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income	$ 72,547	$ 40,128	$ 32,442
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	15,730	8,525	5,765
Deferred income taxes	5,240	788	3,543
Equity-based compensation expenses	1,052	911	690
Impairment	0	0	2,073
Deferred financing costs amortization and other	127	0	0
Working capital changes:
Change in accounts and insurance receivable	(56,473)	(2,908)	(9,482)
Change in inventory	(94)	0	0
Change in prepaid expenses	(304)	(623)	(358)
Change in current income taxes payable	17,618	24,069	16,796
Change in accounts payable and accrued liabilities	24,400	1,196	2,674
Net cash provided by operating activities	79,843	72,086	54,143
Cash flows from investing activities:
Capital expenditures	(181,424)	(157,866)	(120,234)
Acquisitions	(74,520)	0	0
Net cash used in investing activities	(255,944)	(157,866)	(120,234)
Cash flows from financing activities:
Capital contributions from parent prior to the initial public offering	65,145	85,780	66,091
Capital contributions from non-controlling interests	33,875	0	0
Proceeds from initial public offering, net of offering costs	134,185	0	0
Distribution to Oasis Petroleum subsequent to the initial public offering	(132,083)	0	0
Revolving Credit Facility origination fees and expenses paid	(2,138)	0	0
Proceeds from Revolving Credit Facility	78,000	0	0
Net cash provided by financing activities	176,984	85,780	66,091
Increase in cash and cash equivalents	883	0	0
Beginning of period	0	0	0
End of period	883	0	0
Supplemental non-cash transactions:
Change in accrued capital expenditures	63,199	16,434	(19,098)
Change in asset retirement obligations	198	351	(283)
Installment notes from acquisition	4,875	0	0
Cash paid for interest	456	0	0
Non-cash elimination of current and deferred tax liabilities	$ 104,005	$ 0	$ 0

Organization and Nature of Oper

Organization and Nature of Operations	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Nature of Operations	Organization and Nature of Operations Organization. Oasis Midstream Partners LP (the “Partnership” or “Oasis Midstream”) is a growth-oriented, fee-based master limited partnership formed by its sponsor, Oasis Petroleum Inc. (together with its subsidiaries, “Oasis Petroleum”) to own, develop, operate and acquire a diversified portfolio of midstream assets in North America that are integral to the oil and natural gas operations of Oasis Petroleum and are strategically positioned to capture volumes from other producers. Initial public offering. On September 25, 2017, the Partnership completed its initial public offering (the “Offering”) of 7,500,000 common units representing limited partner interests in the Partnership at a price to the public of $17.00 per common unit ($ 15.98 per common unit, net of underwriting discounts and commissions). Additionally, on October 10, 2017, the Partnership issued an additional 1,125,000 common units representing limited partner interests in the Partnership, pursuant to the underwriters’ over-allotment option at the same price and on the same terms. The Partnership received net proceeds of approximately $134.2 million , after deducting underwriting discounts, structuring fees and transaction costs. The Partnership distributed net proceeds of approximately $132.1 million to Oasis Petroleum. The Offering was pursuant to the Partnership’s registration statement on Form S-1, as amended, filed with the Securities and Exchange Commission (“SEC”) and declared effective on September 20, 2017. The common units are traded on the New York Stock Exchange under the symbol OMP. Contributed businesses. The Partnership conducts its business through its ownership of development companies Bighorn DevCo LLC (“Bighorn DevCo”), Bobcat DevCo LLC (“Bobcat DevCo”) and Beartooth DevCo LLC (“Beartooth DevCo,” and collectively with Bighorn DevCo and Bobcat DevCo, the “DevCos”), two of which are jointly-owned with Oasis Petroleum. In connection with the Offering, Oasis Petroleum contributed to the Partnership ownership interests in the following DevCos: DevCos Areas Served Service Lines Oasis Midstream Ownership Bighorn DevCo Wild Basin – Gas processing – Crude stabilization – Crude blending – Crude storage – Crude transportation 100% Bobcat DevCo Wild Basin – Gas gathering – Gas compression – Gas lift – Crude gathering – Produced and flowback water gathering – Produced and flowback water disposal 10% Beartooth DevCo Alger – Produced and flowback water gathering – Produced and flowback water disposal – Freshwater supply and distribution 40% In exchange for the contribution of ownership interests in the DevCos, Oasis Petroleum received 5,125,000 common units and 13,750,000 subordinated units, representing a limited partner interest in the Partnership and the right to receive cash distributions from the Partnership. In addition to and concurrent with the closing of the Offering, the Partnership’s general partner, OMP GP LLC (the “General Partner”), retained a non-economic general partnership interest and was issued incentive distribution rights in the Partnership (the “IDRs”). Nature of business. The Partnership operates in two primary areas with developed midstream infrastructure, both of which are supported by significant acreage dedications from Oasis Petroleum. In Wild Basin, Oasis Petroleum has dedicated to the Partnership approximately 65,000 acres, of which approximately 29,000 acres are within Oasis Petroleum’s current gross operated acreage position, and in which the Partnership has the right to provide oil, gas and water services to support Oasis Petroleum’s existing and future production. In addition, Oasis Petroleum has dedicated to the Partnership approximately 581,000 acres and 364,000 acres for produced and flowback water services and freshwater services, respectively, of which approximately 299,000 acres and 203,000 acres, respectively, are within Oasis Petroleum’s current gross operated acreage. The Partnership generates substantially all of its revenues through long-term, fee-based contractual arrangements with wholly owned subsidiaries of Oasis Petroleum for midstream services. These services include (i) gas gathering, compression, processing and gas lift services; (ii) crude gathering, stabilization, blending, storage and transportation services; (iii) produced and flowback water gathering and disposal services; and (iv) freshwater supply and distribution services. The revenue earned from these services is generally directly related to the volume of natural gas, crude oil and water that flows through Oasis Midstream’s systems, and Oasis Midstream generally does not take ownership to the crude oil or natural gas that it handles for its customers, including Oasis Petroleum. Predecessor. Prior to September 25, 2017, Oasis Petroleum’s midstream services were performed by Oasis Midstream Services LLC (“OMS”), which constitutes the predecessor to the Partnership for accounting purposes (the “Predecessor”). The consolidated financial statements include the results of the Predecessor for the periods presented prior to the Offering on September 25, 2017 . Certain midstream infrastructure assets, liabilities, revenues and expenses included in the Predecessor’s historical financial statements have been excluded from the businesses of the DevCos upon formation. These excluded assets are not included in the consolidated financial statements for the periods presented subsequent to the Offering on September 25, 2017 . Substantially all of the services of the Predecessor were provided to Oasis Petroleum North America LLC (“OPNA”), a wholly owned subsidiary of Oasis Petroleum that conducts Oasis Petroleum’s oil and natural gas exploration and production (“E&P”) activities. The Predecessor financial statements have been prepared from the separate records maintained by Oasis Petroleum and may not necessarily be indicative of the actual results of operations that might have occurred if the Predecessor had been operated separately during the periods reported.

Summary of Significant Accounti

Summary of Significant Accounting Policies and Basis of Presentation	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies and Basis of Presentation	Summary of Significant Accounting Policies and Basis of Presentation Basis of Presentation The accompanying consolidated financial statements of the Partnership include the accounts of Oasis Midstream Partners LP and its subsidiaries. All significant intercompany transactions have been eliminated in consolidation. These statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). Use of Estimates Preparation of the Partnership’s consolidated financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ significantly from those estimates. Management evaluates estimates and assumptions on an ongoing basis using historical experience and other factors, including the current economic and commodity price environment. Consolidation The Partnership’s consolidated financial statements include its accounts and the accounts of the DevCos, each of which is controlled by the general partner of the Partnership. All intercompany balances and transactions have been eliminated upon consolidation. Variable interest entities. With respect to Bobcat DevCo and Beartooth DevCo, management has determined that OMS’s equity at risk was established with non-substantive voting rights, making Bobcat DevCo and Beartooth DevCo variable interest entities (“VIEs”) under the rules of the Financial Accounting Standards Board (“FASB”). Through its 100% ownership interest in OMP Operating LLC (“OMP Operating”), which owns controlling interests in Bobcat DevCo and Beartooth DevCo, the Partnership has the authority to direct the activities that most significantly affect the economic performance of these entities and the obligation to absorb losses or the right to receive benefits that could be potentially significant to them. Therefore, the Partnership is considered the primary beneficiary of Bobcat DevCo and Beartooth DevCo and is required to consolidate these entities in its financial statements under the VIE consolidation model. The Partnership has determined that Bighorn DevCo is not a VIE due to OMP Operating’s 100% ownership interest in Bighorn DevCo, which is proportional to its voting rights through its controlling interest. The Partnership has a controlling financial interest in Bighorn DevCo, through its 100% ownership interest in OMP Operating, and is required to consolidate Bighorn DevCo in its financial statements under the voting interest consolidation model. Non-controlling interests. The non-controlling interests represent Oasis Petroleum’s retained ownership interest in Bobcat DevCo and Beartooth DevCo of 90% and 60% , respectively. Significant Accounting Policies Revenue recognition. The Partnership generates revenue primarily by charging fees for midstream services for (i) crude oil gathering, stabilization, blending, storage and transportation, (ii) natural gas gathering, gas lift, compression and processing, (iii) produced and flowback water gathering and disposal and (iv) freshwater supply and distribution. The Partnership recognizes revenue when services have been rendered, the prices are fixed or determinable, and collectability is reasonable assured. Cash and cash equivalents. The Partnership classifies all unrestricted cash on hand and investments with original maturity dates less than 90 days as cash equivalents. Transactions with affiliates. Transactions between Oasis Petroleum, its affiliates and the Partnership have been identified in the consolidated financial statements as transactions with affiliates. See Note 3 . Transactions with Affiliates . Property, plant and equipment. Property, plant and equipment consists primarily of pipelines, Gas Plant I, produced and flowback water facilities and compressor stations. Property, plant and equipment is stated at the lower of historical cost less accumulated depreciation, or fair value, if impaired. The Partnership capitalizes a portion of its interest expense incurred on its outstanding debt. The amount capitalized is determined by multiplying the capitalization rate by the average amount of eligible accumulated capital expenditures and is limited to actual interest costs incurred during the period. The accumulated capital expenditures included in the capitalized interest calculation begin when the first costs are incurred and end when the asset is either placed into production or written off. The Partnership capitalized $1.2 million , $4.4 million and $2.9 million of interest costs for the years ended December 31, 2017 , 2016 and 2015 , respectively. These amounts are amortized over the useful life of the related assets once the assets are placed in-service. When assets are placed into service, management makes estimates with respect to useful lives and salvage values that management believes are reasonable. However, subsequent events could cause a change in estimates, thereby impacting future depreciation amounts. Uncertainties that may impact these estimates include, among others, changes in laws and regulations relating to environmental matters, including air and water quality, restoration and abandonment requirements, economic conditions and supply and demand in the area. Depreciation is computed over the asset’s estimated useful life using the straight line method based on estimated useful lives and asset salvage values. The weighted average life of each of our pipelines, natural gas processing plant, produced and flowback water facilities, compressor stations, and other long-lived assets is 30 years. When properties are retired or otherwise disposed of, the related cost and accumulated depreciation are removed from the respective accounts and any profit or loss on disposition is recognized as gain or loss. Impairment of long-lived assets. The Partnership evaluates the ability to recover the carrying amount of long-lived assets and determine whether such long-lived assets have been impaired. Impairment exists when the carrying amount of an asset exceeds estimates of the undiscounted cash flows expected to result from the use and eventual disposition of the asset. An impairment analysis requires management to apply judgment in identifying impairment indicators and estimating future cash flows. When alternative courses of action to recover the carrying amount of a long-lived asset are under consideration, estimates of future undiscounted cash flows take into account possible outcomes and probabilities of their occurrence. If the carrying amount of the long-lived asset is not recoverable based on the estimated future undiscounted cash flows, the impairment loss is measured as the excess of the asset’s carrying amount over its estimated fair value, such that the asset’s carrying amount is adjusted to its estimated fair value with an offsetting charge to impairment expense. Fair value represents the estimated price between market participants to sell an asset in the principal or most advantageous market for the asset, based on assumptions a market participant would make. When warranted, management assesses the fair value of long-lived assets using commonly accepted techniques and may use more than one source in making such assessments. The factors used to determine fair value are subject to management’s judgment and expertise and include, but are not limited to, recent third-party comparable sales, internally developed discounted cash flow analysis and analysis from outside advisors. Significant changes, such as changes in contract rates or terms, the condition of an asset or management’s intent to utilize the asset, generally require management to reassess the cash flows related to long-lived assets. A reduction of the carrying value of fixed assets would represent a Level 3 fair value measurement. If actual results are not consistent with our assumptions and estimates or our assumptions and estimates change due to new information, we may be exposed to additional impairment charges. Ultimately, a prolonged period of lower commodity prices may adversely affect the estimate of future operating results through lower throughput volumes on the Partnership’s assets, which could result in future impairment charges due to the potential impact on operations and cash flows. Asset retirement obligations (“ARO”). The Partnership records the fair value of a liability for a legal obligation to retire an asset in the period in which the liability is incurred, with the corresponding cost capitalized by increasing the carrying amount of the related long-lived asset. For produced and flowback water disposal wells, this is the period in which the well is drilled or acquired. The ARO represents the estimated amount we will incur to plug, abandon and remediate the produced and flowback water properties at the end of their useful lives, in accordance with applicable state laws. The liability is accreted to its present value each period and the capitalized costs are depreciated using the straight-line method. The accretion expense is recorded as a component of depreciation and amortization in the Consolidated Statements of Operations. Some assets, including certain pipelines and the natural gas processing plant, have contractual or regulatory obligations to perform remediation and, in some instances, dismantlement and removal activities when the assets are abandoned. The Partnership is not able to reasonably estimate the fair value of the ARO for these assets because the settlement dates are indeterminable given the expected continued use of the assets with proper maintenance. The Partnership will record an ARO for these assets in the periods in which the settlement dates become reasonably determinable. The Partnership determines the ARO, which represents a non-financial liability which is measured at fair value on a non-recurring basis, by calculating the present value of estimated cash flows related to the liability. Estimating the future ARO requires management to make estimates and judgments regarding timing and existence of a liability, as well as what constitutes adequate restoration. Inherent in the fair value calculation are numerous assumptions and judgments including the ultimate costs, inflation factors, credit adjusted discount rates, timing of settlement and changes in the legal, regulatory, environmental and political environments. These assumptions represent Level 3 inputs. To the extent future revisions to these assumptions impact the fair value of the existing ARO liability, a corresponding adjustment is made to the related asset. Deferred financing costs. The Partnership capitalizes directly attributable costs incurred in connection with obtaining debt financing. These costs are amortized over the term of the related financing using the straight-line method, which approximates the interest method. The amortization expense is recorded as a component of interest expense in the Partnership’s Consolidated Statements of Operations. The deferred financing costs related to the Partnership’s Revolving Credit Facility are included in other assets on the Partnership’s Consolidated Balance Sheets. Unit-based compensation. The Partnership has granted phantom unit awards and restricted unit awards under the Oasis Midstream Partners LP 2017 Long Term Incentive Plan (“LTIP”). The Partnership accounts for phantom unit awards as liability-classified awards in accordance with GAAP, since the Partnership intends to settle these awards in cash. The Partnership will be reimbursed by Oasis Petroleum for the cash settlement amount of these awards. The Partnership accounts for restricted units granted to certain directors of the Partnership as equity-classified awards in accordance with GAAP, as the Partnership intends to settle these awards in common units. Income taxes. For the period subsequent to the Offering, the consolidated financial statements do not include a provision for income taxes as the Partnership is generally not subject to federal or state income tax. Generally, each partner is separately taxed on its share of taxable income. For periods prior to the Offering, the consolidated financial statements include a provision for income tax expense. Deferred federal and state income taxes were provided on temporary differences between the financial statement carrying amounts of recognized assets and liabilities and their respective tax bases as if the Partnership filed tax returns as a stand-alone entity. Business combinations. The Partnership accounts for business combinations under the acquisition method of accounting. An income, market or cost valuation method may be utilized to estimate the fair value of the assets acquired, liabilities assumed, and non-controlling interest, if any, in a business combination. Fair value is determined on the acquisition date. Acquisition-related costs are expensed as incurred in connection with each business combination. If the initial accounting for the business combination is incomplete by the end of the reporting period in which the acquisition occurs, an estimate will be recorded. Subsequent to the acquisition, and not later than one year from the acquisition date, the Partnership will record any material adjustments to the initial estimate based on new information obtained about facts and circumstances that existed as of the acquisition date. The Partnership makes various assumptions in estimating the fair values of assets acquired and liabilities assumed. As fair value is a market-based measurement, it is determined based on the assumptions that market participants would use. The income valuation method represents the present value of future cash flows over the life of the asset using discrete financial forecasts. Such discrete financial forecasts rely on estimates and assumptions made by management. The most significant assumptions relate to management’s estimates of throughput volumes, future operating and development costs, long-term growth rates and a market-based weighted average cost of capital. The market valuation method uses prices paid for a reasonably similar asset by other purchasers in the market, with adjustments relating to any differences between the assets. The cost valuation method is based on the replacement cost of a comparable asset at prices at the time of the acquisition reduced for depreciation of the asset. Any excess of the acquisition price over the estimated fair value of net assets acquired is recorded as goodwill. Any excess of the estimated fair value of net assets acquired over the acquisition price is recorded in current earnings as a gain on bargain purchase. Concentrations of Market and Credit Risk The Partnership has limited direct exposure to risks associated with fluctuating commodity prices due to the nature of its business and its long-term, fixed-fee arrangements with Oasis Petroleum. However, to the extent that the future contractual arrangements with Oasis Petroleum or third parties do not provide for fixed-fee structures, the Partnership may become subject to commodity price risk. Additionally, as substantially all of the Partnership’s revenues are derived from Oasis Petroleum, the Partnership is indirectly subject to risks associated with fluctuating commodity prices to the extent that lower commodity prices adversely affect Oasis Petroleum’s production, drilling schedule, financial condition, leverage, market reputation, liquidity, results of operations or cash flows. Recent Accounting Pronouncements Revenue Recognition In May 2014, the FASB issued Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (“ASU 2014-09”). The objective of ASU 2014-09 is greater consistency and comparability across industries by using a five-step model to recognize revenue from customer contracts. ASU 2014-09 also contains enhanced disclosure requirements under GAAP. In August 2015, the FASB issued Accounting Standards Update No. 2015-14, Deferral of the Effective Date (“ASU 2015-14”). ASU 2015-14 defers the effective date of the new revenue standard by one year, making it effective for annual reporting periods beginning after December 15, 2017, including interim periods within that reporting period. In 2016 and 2017, the FASB issued additional accounting standards updates to clarify the implementation guidance of ASU 2014-09. During 2017, the Partnership completed its analysis of the impact of the standard on its contract types comprising each of its significant revenue streams, and it does not believe that the adoption of ASU 2014-09 has a material impact on its financial position, cash flows and results of operations but could impact certain disclosures. The Partnership has also modified current processes and controls to apply the requirements of the new standard and does not believe such modifications are material to its internal controls over financial reporting. Leases In February 2016, the FASB issued Accounting Standards Update No. 2016-02, Leases (“ASU 2016-02”), which requires a lessee to recognize lease payment obligations and a corresponding right-of-use asset to be measured at fair value on the balance sheet. ASU 2016-02 also requires certain qualitative and quantitative disclosures about the amount, timing and uncertainty of cash flows arising from leases. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018, including interim periods within those years. Also, in January 2018, the FASB issued Accounting Standards Update No. 2018-01, Land easement practical expedient for transition to Topic 842 (“ASU 2018-01”), which provides an optional transition practical expedient to not evaluate under Topic 842 existing or expired land easements that were not previously accounted for as leases under Topic 840, Leases. The Partnership plans to elect this practical expedient and is currently evaluating the effect that adopting the new lease guidance will have on its financial position, cash flows and results of operations. Statement of Cash Flows In August 2016, the FASB issued Accounting Standards Update No. 2016-15, Statement of Cash Flows (“ASU 2016-15”), which is intended to reduce diversity in practice in how certain transactions are classified in the statement of cash flows. ASU 2016-15 is effective for fiscal years beginning after December 15, 2017, including interim periods within those years, and is required to be applied under the retrospective method. The Partnership will adopt the new standard on the effective date of January 1, 2018. The Partnership does not expect the adoption of this guidance to have a material impact on its financial position, cash flows or results of operations. Income Taxes In October 2016, the FASB issued Accounting Standards Update No. 2016-16, Intra-Entity Transfers of Assets Other Than Inventory (“ASU 2016-16”), to improve the accounting for the income tax consequences of intra-entity transfers of assets other than inventory. ASU 2016-16 is effective for fiscal years beginning after December 15, 2017, including interim periods within those years, and is required to be applied on a modified retrospective basis. The Partnership will adopt the new standard on the effective date of January 1, 2018. The Partnership does not expect the adoption of this guidance to have a material impact on its financial position, cash flows or results of operations. Business Combinations In January 2017, the FASB issued Accounting Standards Update No. 2017-01, Clarifying the Definition of a Business (“ASU 2017-01”), which provides guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. ASU 2017-01 requires entities to use a screen test to determine when an integrated set of assets and activities is not a business or if the integrated set of assets and activities needs to be further evaluated against the framework. ASU 2017-01 is effective for fiscal years beginning after December 15, 2017, including interim periods within those years, and is required to be applied prospectively. The Partnership will adopt the new standard on the effective date of January 1, 2018. The Partnership does not expect the adoption of this guidance to have a material impact on its financial position, cash flows or results of operations. Equity-Based Compensation In May 2017, the FASB issued Accounting Standards Update No. 2017-09, Scope of Modification Accounting (“ASU 2017-09”), which provides guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting. ASU 2017-09 is effective for annual periods beginning after December 15, 2017, including interim periods within those years, and is required to be applied prospectively. The Partnership will adopt the new standard on the effective date of January 1, 2018. The Partnership does not expect the adoption of this guidance to have a material impact on its financial position, cash flows or results of operations.

Transactions with Affiliates

Transactions with Affiliates	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Transactions with Affiliates	Transactions with Affiliates Revenues. The Partnership generates substantially all of its revenues through 15 -year, fee-based contractual arrangements with wholly owned subsidiaries of Oasis Petroleum for midstream services. These services include (i) gas gathering, compression, processing and gas lift services; (ii) crude gathering, stabilization, blending, storage and transportation services; (iii) produced and flowback water gathering and disposal services; and (iv) freshwater supply and distribution services. The revenue earned from these services is generally directly related to the volume of natural gas, crude oil and produced and flowback water that flows through the Partnership’s systems, and the Partnership generally does not take ownership of the crude oil or natural gas that it handles for its customers, including Oasis Petroleum. Expenses. Oasis Petroleum provides substantial labor and overhead support for the Partnership. Upon completion of the Offering, the Partnership entered into a 15 -year services and secondment agreement with Oasis Petroleum pursuant to which Oasis Petroleum provides all personnel, equipment, electricity, chemicals and services (including third-party services) required for the Partnership to operate such assets, and the Partnership reimburses Oasis Petroleum for its share of the actual costs of operating such assets. In addition, pursuant to the services and secondment agreement, Oasis Petroleum performs centralized corporate, general and administrative services for the Partnership, such as legal, corporate recordkeeping, planning, budgeting, regulatory, accounting, billing, business development, treasury, insurance administration and claims processing, risk management, health, safety and environmental, information technology, human resources, investor relations, cash management and banking, payroll, internal audit, taxes and engineering. Oasis Petroleum has also seconded to the Partnership certain of its employees to operate, construct, manage and maintain its assets, and the Partnership reimburses Oasis Petroleum for direct general and administrative expenses incurred by Oasis Petroleum for the provision of the above services. The expenses of executive officers and non-executive employees of Oasis Petroleum are allocated to the Partnership based on the amount of time spent managing the Partnership’s business and operations. For the periods prior to the Offering, shared services and direct labor were allocated to the Predecessor primarily based on headcount and direct usage during the respective years. Management believes that these allocations are reasonable and reflect the utilization of services provided and benefits received, but may differ from the cost that would have been incurred had the Predecessor operated as a stand-alone company for the periods presented prior to the Offering. Additionally, for the periods prior to September 25, 2017 , the accompanying Consolidated Statements of Operations include interest expense recognized by the Predecessor related to its funding activity with Oasis Petroleum based on capital expenditures for the period using the weighted average effective interest rate for Oasis Petroleum’s long-term indebtedness. Operating expenses incurred from transactions with Oasis Petroleum are shown below for the periods presented: Year Ended December 31, 2017 2016 2015 Operating expenses (1) General and administrative $ 12,828 $ 7,821 $ 6,140 Interest expense, net of capitalized interest 6,945 5,481 4,514 ___________________ (1) Transactions between the Predecessor and Oasis Petroleum are shown above for the periods prior to the Offering on September 25, 2017 .

Accrued Liabilities

Accrued Liabilities	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued Liabilities	Accrued Liabilities Accrued liabilities consist of the following: December 31, 2017 December 31, 2016 (In thousands) Accrued capital costs $ 47,843 $ 27,085 Accrued operating expenses 10,860 3,913 Other accrued liabilities 115 1,181 Total accrued liabilities (1) $ 58,818 $ 32,179 ___________________ (1) Accrued liabilities as of December 31, 2017 represent the obligations of the Partnership subsequent to the Offering, while accrued liabilities as of December 31, 2016 represent the obligations of the Predecessor.

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, Plant and Equipment Property, plant and equipment consists of the following: December 31, 2017 December 31, 2016 (In thousands) Pipelines $ 255,231 $ 199,943 Natural gas processing plant 102,371 92,630 Produced and flowback water facilities 80,050 75,828 Compressor stations 59,293 35,507 Other property and equipment 32,340 31,039 Construction in progress 124,643 18,748 Total property, plant and equipment 653,928 453,695 Less: accumulated depreciation and amortization (34,348 ) (22,160 ) Total property, plant and equipment, net $ 619,580 $ 431,535 Acquisition. On April 25, 2017, the Predecessor completed purchase and sale agreements with two undisclosed private sellers to acquire certain midstream assets in McKenzie County, North Dakota for total consideration of $12.7 million , which includes $4.9 million of installment notes. Based on the FASB’s authoritative guidance, the acquisition qualified as a business combination, and as such, the Predecessor estimated the fair value of the assets acquired as of the acquisition date. The Predecessor recorded the assets acquired at their estimated fair value of $12.7 million , which is representative of the price paid by a typical market participant. This measurement resulted in no goodwill or bargain purchase being recognized. In connection with the closing of the Offering, these assets were contributed to the Partnership. The results of operations for the acquisition have been included in the consolidated financial statements since the closing date. Pro forma information is not presented as the pro forma results would not be materially different from the information presented in the Consolidated Statements of Operations. Gas Plant II Assignment. On November 6, 2017, Oasis Petroleum agreed to assign to the Partnership the second Wild Basin gas plant (“Gas Plant II”). The Gas Plant II project was under construction at December 31, 2017 , and the Partnership anticipates operations will begin in late 2018. In exchange for the assignment of Gas Plant II into Bighorn DevCo, the Partnership agreed to reimburse Oasis Petroleum for 100% of its capital spent through the date of assignment of $66.7 million . The Partnership funded the reimbursement with proceeds from its Revolving Credit Facility (as defined below). The Partnership accounted for the Gas Plant II assignment at its historical basis in accordance with the GAAP for the transfer of an asset between entities under common control. The Partnership determined the Gas Plant II assignment did not represent a change in reporting entity, as the assignment did not involve the transfer of a business. Since there was no change in reporting entity, the Partnership did not retrospectively adjust its historical financial statements for the periods presented prior to the assignment.

Long-Term Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Long-Term Debt	Long-Term Debt On September 25, 2017, the Partnership entered into a credit agreement (the “Credit Agreement”) for a $200.0 million revolving credit facility with OMP Operating as borrower (the “ Revolving Credit Facility ”), which has a maturity date of September 25, 2022. The Revolving Credit Facility is available to fund working capital and to finance acquisitions and other capital expenditures of the Partnership. The Revolving Credit Facility includes a letter of credit sublimit of $10.0 million and a swingline loans sublimit of $10.0 million . The borrowing capacity on the Revolving Credit Facility may be increased up to $400.0 million , subject to certain conditions. All obligations of OMP Operating, as the borrower under the Revolving Credit Facility, are unconditionally guaranteed on a joint and several basis by the Partnership, OMP Operating and Bighorn DevCo. At December 31, 2017 , $78.0 million of borrowings were outstanding under the Revolving Credit Facility. The Revolving Credit Facility is collateralized by mortgages and other security interests on substantially all of the Partnership’s and its subsidiaries’ properties and assets, including the equity interests in all present and future subsidiaries (subject to certain exceptions). Some or all of the collateral owned by Bobcat DevCo and Beartooth DevCo is subject to an intercreditor agreement between Wells Fargo, National Association (“Wells Fargo”), as administrative agent for the Revolving Credit Facility and Wells Fargo as the administrative agent for the revolving credit facility of Oasis Petroleum, and acknowledged by OMS, Bobcat DevCo and Beartooth DevCo. The Revolving Credit Facility provides for customary representations, warranties and covenants, including, among other things, covenants relating to financial and collateral reporting, notices of material events, maintenance of the existence of the business and its properties, payment of obligations, the Partnership’s ability to enter into certain hedging agreements, limitations on the Partnership’s ability to sell or acquire properties and limitations on indebtedness and liens, dividends and distributions, transactions with affiliates and certain fundamental transactions. Borrowings under the Revolving Credit Facility bear interest at a rate per annum equal to the applicable margin (as described below) plus (i) with respect to Eurodollar Loans, the Adjusted LIBO Rate (as defined in the Credit Agreement) or (ii) with respect to ABR Loans, the greatest of (A) the Prime Rate in effect on such day, (B) the Federal Funds Effective Rate in effect on such day plus 1/2 of 1.00% or (C) the Adjusted LIBO Rate for a one-month interest period on such day plus 1.00% (each as defined in the Credit Agreement). The applicable margin for borrowings under the Revolving Credit Facility varies from (a) in the case of Eurodollar Loans, 1.75% to 2.75% , and (b) in the case of ABR Loans or swingline loans, 0.75% to 1.75% . The unused portion of the Revolving Credit Facility is subject to a commitment fee ranging from 0.375% to 0.500% . As of December 31, 2017 , any outstanding ABR or Eurodollar loans would have borne their respective interest rates plus the applicable margin indicated in the following table: Consolidated Total Leverage Ratio Applicable Margin for Eurodollar Loans Applicable Margin for ABR Loans Commitment Fee Rate Less than or equal to 3.00 to 1.00 1.75 % 0.75 % 0.375 % Greater than 3.00 to 1.00 but less than or equal to 3.50 to 1.00 2.00 % 1.00 % 0.375 % Greater than 3.50 to 1.00 but less than or equal to 4.00 to 1.00 2.25 % 1.25 % 0.500 % Greater than 4.00 to 1.00 but less than or equal to 4.50 to 1.00 2.50 % 1.50 % 0.500 % Greater than 4.50 to 1.00 2.75 % 1.75 % 0.500 % The Revolving Credit Facility also requires the Partnership to maintain the following financial covenants as of the end of each fiscal quarter: • Consolidated Total Leverage Ratio: Prior to the date on which one or more of the credit parties have issued an aggregate principal amount of at least $150.0 million of senior notes (as permitted under the Revolving Credit Facility) (such date the “Covenant Changeover Date”) and commencing with the fiscal quarter ended December 31, 2017 , the Partnership and OMP Operating’s ratio of Total Debt to EBITDA (each as defined in the Credit Agreement) on a quarterly basis may not exceed 4.50 to 1.00 (or during an Acquisition Period (as defined in the Credit Agreement), 5.00 to 1.00 ). On a quarterly basis following the Covenant Changeover Date, the Partnership and OMP Operating’s ratio of Total Debt to EBITDA may not exceed 5.25 to 1.00. • Consolidated Senior Secured Leverage Ratio: On a quarterly basis, commencing with the date the Covenant Changeover Date occurs, the Partnership and OMP Operating’s ratio of Consolidated Senior Secured Funded Debt to EBITDA (each as defined in the Credit Agreement) may not exceed 3.75 to 1.00 . • Consolidated Interest Coverage Ratio: On a quarterly basis prior to the Covenant Changeover Date and commencing with the fiscal quarter ended December 31, 2017 , the Partnership and OMP Operating’s ratio of EBITDA to Consolidated Interest Expense (each as defined in the Credit Agreement) may not be less than 3.00 to 1.00 and on a quarterly basis following the Covenant Changeover Date, the Partnership and OMP Operating’s ratio of EBITDA to Consolidated Interest Expense may not be less than 2.50 to 1.00 The Partnership was in compliance with the financial covenants of the Revolving Credit Facility at December 31, 2017 .

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Partnership is not a taxable entity for U.S. federal income tax purposes, and taxes are generally borne by unitholders through the allocation of taxable income. In connection with the Offering, Predecessor current and deferred tax liabilities of $104.0 million were eliminated upon consummation of the Partnership. At December 31, 2017 , the net difference between the tax bases and reported amounts of the Partnership’s assets and liabilities is $31.7 million . The provision for income taxes included in the Consolidated Statements of Operations for the periods presented relates to the Predecessor. The Predecessor is not a separate taxable entity for U.S. federal and certain states purposes, and its results are included in the consolidated income tax returns of Oasis Petroleum. The provision for income taxes recorded by the Predecessor was determined as if the Predecessor was a stand-alone taxpayer for the period prior to the Offering on September 25, 2017 . The Predecessor’s income tax expense consists of the following: December 31, 2017 2016 2015 Current: Federal $ 15,571 $ 21,272 $ 14,811 State 2,047 2,797 1,985 17,618 24,069 16,796 Deferred: Federal 4,631 772 3,191 State 609 16 352 5,240 788 3,543 Total income tax expense $ 22,858 $ 24,857 $ 20,339 The reconciliation of income taxes calculated at the U.S. federal statutory rate to the Predecessor’s effective tax rate for the years presented is as follows: December 31, 2017 2016 2015 (%) (In thousands) (%) (In thousands) (%) (In thousands) U.S. federal statutory rate 35.00 % 33,392 35.00 % 22,745 35.00 % 18,648 Earnings not subject to tax subsequent to the Offering (12.83 )% (12,239 ) — % — — % — State income taxes, net of federal income tax benefit 1.81 % 1,727 2.90 % 1,882 2.94 % 1,565 Other (0.02 )% (22 ) 0.35 % 230 0.23 % 126 Annual effective tax rate 23.96 % 22,858 38.25 % 24,857 38.17 % 20,339

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies The Partnership has various contractual obligations in the normal course of its operations. Currently, there are no unrecorded commitments in the accompanying Consolidated Balance Sheets as of December 31, 2017 . Operating lease. The Partnership has leases for certain machinery and equipment used in its operations, which it accounts for as operating leases in accordance with GAAP. For the year ended December 31, 2017 , rental expense of $1.8 million is included in direct operating expenses on the Consolidated Statements of Operations. Future minimum rental payments at December 31, 2017 are as follows: (In thousands) 2018 $ 4,372 2019 292 2020 — 2021 — 2022 — Thereafter — $ 4,664 Purchase commitments. The Partnership is party to certain contractual agreements to purchase a minimum quantity of freshwater. Future commitments at December 31, 2017 are as follows: (In thousands) 2018 $ 373 2019 400 2020 414 2021 1,200 2022 — Thereafter — $ 2,387 Litigation. The Partnership is party to various legal and/or regulatory proceedings from time to time arising in the ordinary course of business. When the Partnership determines that a loss is probable of occurring and is reasonably estimable, the Partnership accrues an undiscounted liability for such contingencies based on its best estimate using information available at the time. The Partnership discloses contingencies where an adverse outcome may be material, or where in the judgment of management, the matter should otherwise be disclosed. Mirada litigation. On March 23, 2017, Mirada filed a lawsuit against Oasis Petroleum, OPNA, and OMS, seeking monetary damages in excess of $100.0 million , declaratory relief, attorneys’ fees and costs (Mirada Energy, LLC, et al. v. Oasis Petroleum North America LLC, et al.; in the 334th Judicial District Court of Harris County, Texas; Case Number 2017-19911). In its original lawsuit, Mirada asserts that it is a working interest owner in certain acreage owned and operated by Oasis Petroleum in Wild Basin. Specifically, Mirada asserts that Oasis Petroleum has breached certain agreements by: (1) failing to allow Mirada to participate in Oasis Petroleum’s midstream operations in Wild Basin; (2) refusing to provide Mirada with information that Mirada contends is required under certain agreements and failing to provide information in a timely fashion; (3) failing to consult with Mirada and failing to obtain Mirada’s consent prior to drilling more than one well at a time in Wild Basin; and (4) by overstating the estimated costs of proposed well operations in Wild Basin. Mirada seeks a declaratory judgment that OPNA be removed as operator in Wild Basin at Mirada’s election and that Mirada be allowed to elect a new operator; that certain agreements apply to Oasis Petroleum and Mirada and Wild Basin with respect to this dispute; that Oasis Petroleum be required to provide all information within its possession regarding proposed or ongoing operations in Wild Basin; and that OPNA not be permitted to drill, or propose to drill, more than one well at a time in Wild Basin without obtaining Mirada’s consent. Mirada also seeks a declaratory judgment with respect to Oasis Petroleum’s current midstream operations in Wild Basin. Specifically, Mirada seeks a declaratory judgment that Mirada has a right to participate in Oasis Petroleum’s Wild Basin midstream operations, consisting of produced and flowback water disposal, crude oil gathering and gas gathering and processing; that, upon Mirada’s election to participate, Mirada is obligated to pay its proportionate costs of Oasis Petroleum’s midstream operations in Wild Basin; and that Mirada would then be entitled to receive a share of revenues from the midstream operations and would not be charged any amount for its use of these facilities for production from the “Contract Area.” On June 30, 2017, Mirada amended its original petition to add a claim that Oasis Petroleum has breached certain agreements by charging Mirada for midstream services provided by its affiliates and to seek a declaratory judgment that Mirada is entitled to be paid its share of total proceeds from the sale of hydrocarbons received by OPNA or any affiliate of OPNA without deductions for midstream services provided by OPNA or its affiliates. On February 2, 2018 and February 16, 2018, Mirada filed a second and third amended petition, respectively. In these filings, Mirada alleges new legal theories for being entitled to enforce the underlying contracts, and added Bighorn DevCo LLC, Bobcat DevCo LLC and Beartooth DevCo LLC as defendants, asserting that these entities were created in bad faith in an effort to avoid contractual obligations owed to Mirada. Mirada may further amend its petition from time to time to assert additional claims as well as defendants. Oasis Petroleum believes that Mirada’s claims are without merit, that Oasis Petroleum has complied with its obligations under the applicable agreements and that some of Mirada’s claims are grounded in agreements which do not apply to Oasis Petroleum. Oasis Petroleum filed an answer denying all of Mirada’s claims and intends and continues to vigorously defend against Mirada’s claims and, to the extent we are made a party to the suit, we intend to vigorously defend ourselves against such claims. Discovery is ongoing, and each of the parties has made a number of procedural filings and motions, and additional filings and motions can be expected over the course of the claim. Although trial is currently scheduled for July 2018, the parties anticipate that the existing trial date will be vacated soon and a new trial date will be selected. However, neither we nor Oasis Petroleum can predict or guarantee the ultimate outcome or resolution of such matter. If such matter were to be determined adversely to our or Oasis Petroleum’s interests, or if we or Oasis Petroleum were forced to settle such matter for a significant amount, such resolution or settlement could have a material adverse effect on our business, results of operations and financial condition. Such an adverse determination could materially impact Oasis Petroleum’s ability to operate its properties in Wild Basin or develop its identified drilling locations in Wild Basin on its current development schedule. A determination that Mirada has a right to participate in Oasis Petroleum’s midstream operations could materially reduce the interests of Oasis Petroleum and us in our current assets and future midstream opportunities and related revenues in Wild Basin. Under the Omnibus Agreement the Partnership entered into with Oasis Petroleum in connection with the closing of our initial public offering, Oasis Petroleum agreed to indemnify the Partnership for any losses resulting from this litigation. However, the Partnership cannot guarantee that such indemnity will fully protect the Partnership from the adverse consequences of any adverse ruling.

Equity-Based Compensation

Equity-Based Compensation	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity-Based Compensation	Equity-Based Compensation Phantom unit awards. On October 19, 2017, the Partnership granted under its LTIP 101,500 phantom unit awards (collectively the “Phantom Units” and each a “Phantom Unit”) to certain employees of Oasis Petroleum who are non-employees of the Partnership. The aggregate number of common units that may be issued under the LTIP is 1,842,500 common units, subject to proportionate adjustment in the event of unit splits and similar events. Each Phantom Unit represents the right to receive a cash payment equal to the fair market value of one common unit on the day prior to the date it vests. Award recipients are also entitled to Distribution Equivalent Rights (a “DER”), which represent the right to receive a cash payment equal to the value of the distributions paid on one common unit between the grant date and the vesting date. The Phantom Units vest in equal amounts each year over a three -year period. The Phantom Units are accounted for as liability-classified awards since the awards will settle in cash, and equity-based compensation cost is accounted for under the fair value method in accordance with GAAP. Under the fair value method for liability-classified awards, compensation cost is remeasured each reporting period at fair value based upon the closing price of a publicly traded common unit. Oasis Petroleum will reimburse the Partnership for the cash settlement amount of these awards. The Partnership recognizes in its Consolidated Balance Sheets the compensation cost associated with these awards in Accounts receivable from Oasis Petroleum and Accrued Liabilities. As of December 31, 2017 , unrecognized compensation cost for all outstanding Phantom Units was $1.6 million , which is expected to be recognized over a weighted average period of 2.8 years. The following table summarizes information related to Phantom Units held by certain non-employees of the Partnership: Phantom Units Weighted Average Grant Date Fair Value per Unit Outstanding at beginning of period — $ — Granted 101,500 16.40 Vested — — Forfeited (2,400 ) 16.40 Outstanding at end of period 99,100 $ 16.40 Restricted unit awards. The Partnership has granted to certain directors 11,766 restricted unit awards under its LTIP, which vest over a one -year period. These awards are accounted for as equity-classified awards since the awards will settle in common units upon vesting. Equity-based compensation cost is accounted for under the fair value method in accordance with GAAP. Under the fair value method for equity-classified awards, compensation cost is measured at the grant date based on the fair value of the award and is recognized over the vesting period. Compensation cost associated with these awards was approximately $0.1 million for the year ended December 31, 2017 and is included in general and administrative expenses on the Consolidated Statements of Operations. As of December 31, 2017 , unrecognized compensation cost for all outstanding restricted unit awards was $0.1 million , which is expected to be recognized over a weighted average period of 0.7 years. The following table summarizes information related to restricted units held by certain directors of the Partnership: Restricted Units Weighted Average Grant Date Fair Value per Unit Outstanding at beginning of period — $ — Granted 11,766 17.00 Vested — — Forfeited — — Outstanding at end of period 11,766 $ 17.00 Restricted stock awards (Predecessor). Prior to the Offering, certain employees of Oasis Petroleum were granted restricted stock awards under its Amended and Restated 2010 Long Term Incentive Plan, the majority of which vest over a three -year period. Oasis Petroleum accounts for these awards as equity-classified awards, in accordance with GAAP. The value of restricted stock grants is based on the closing sales price of Oasis Petroleum’s common stock on the date of grant, and compensation expense is recognized ratably over the requisite service period. The weighted average grant date fair value of restricted stock awards granted to employees of Oasis Petroleum prior to the Offering was $14.95 . In accordance with its indirect shared service expense allocation from Oasis Petroleum, the Predecessor recorded equity-based compensation expense associated with these awards of approximately $1.1 million , $0.9 million and $0.7 million for the year ended December 31, 2017 , 2016 and 2015 , respectively, in general and administrative expenses on the Consolidated Statements of Operations. As of December 31, 2017 , there is no unrecognized expense associated with these awards for the Partnership.

Partnership Equity and Distribu

Partnership Equity and Distributions	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Partnership Equity and Distributions	Partnership Equity and Distributions Minimum quarterly distribution. The partnership agreement requires that all of the Partnership’s available cash be distributed quarterly. Under the current cash distribution policy, the Partnership intends to distribute to the holders of common and subordinated units on a quarterly basis at least the minimum quarterly distribution of $0.3750 per unit, or $1.50 on an annualized basis, to the extent the Partnership has sufficient cash after establishment of cash reserves and payment of fees and expenses, including payments to the general partner and its affiliates. On February 2, 2018 the Board of Directors of the General Partner, declared the initial quarterly cash distribution of $0.3750 per unit for the quarter ended December 31, 2017 . The Board of Directors also declared the third quarter distribution of $0.0245 per unit for the six days ended September 30, 2017. The third quarter distribution was prorated from the closing of the Partnership’s initial public offering on September 25, 2017. Both distributions equate to the minimum quarterly distribution of $0.3750 per unit on a full-quarter basis. Both distributions were paid on February 26, 2018 to unitholders of record as of February 16, 2018 . Subordinated units. Oasis Petroleum owns all of the Partnership’s subordinated units. The partnership agreement provides that, during the subordination period, the common units have the right to receive distributions of available cash from operating surplus each quarter in an amount equal to the minimum quarterly distribution, plus any arrearages in the payment of the minimum quarterly distribution on the common units from prior quarters, before any distributions of available cash from operating surplus may be made on the subordinated units. No arrearages will accrue or be payable on the subordinated units. When the subordination period ends, each outstanding subordinated unit will convert into one common unit and will thereafter participate pro rata with the other common units in distributions of available cash. The subordination period will end on December 31, 2020 after each of the following tests are met: • for each of the three consecutive, non-overlapping four-quarter periods immediately preceding that date, aggregate distributions from operating surplus equaled or exceeded the sum of the minimum quarterly distribution multiplied by the total number of common and subordinated units outstanding in each quarter in each period; • for the same three consecutive, non-overlapping four-quarter periods, the “adjusted operating surplus” (as defined in the Partnership’s Amended and Restated Agreement of Limited Partnership) equaled or exceeded the sum of the minimum quarterly distribution multiplied by the total number of common and subordinated units outstanding during each quarter on a fully diluted weighted average basis; and • there are no arrearages in payment of the minimum quarterly distribution on the common units. Notwithstanding the foregoing, the subordination period will automatically terminate, and all of the subordinated units will convert into common units on a one-for-one basis, on the first business day after the distribution to unitholders in respect of any quarter, beginning with the quarter ended December 31, 2018, if each of the following has occurred: • for one four-quarter period immediately preceding that date, aggregate distributions from operating surplus exceeded 150.0% of the minimum quarterly distribution multiplied by the total number of common units and subordinated units outstanding in each quarter in the period; • for the same four-quarter period, the “adjusted operating surplus” (as defined in the Partnership’s Amended and Restated Agreement of Limited Partnership) equaled or exceeded 150.0% of the sum of the minimum quarterly distribution multiplied by the total number of common and subordinated units outstanding during each quarter on a fully diluted weighted average basis, plus the related distribution on the incentive distribution rights; and • there are no arrearages in payment of the minimum quarterly distributions on the common units. Incentive distribution rights (“IDRs”). The General Partner owns all of the Partnership’s IDRs, which will entitle it to increasing percentages, up to a maximum of 50.0% of the cash the Partnership distributes in excess of $0.43125 per unit per quarter. The maximum distribution of 50.0% does not include any distributions that Oasis Petroleum may receive on common units or subordinated units that it owns. Percentage allocations of available cash from operating surplus. For any quarter in which the Partnership has distributed cash from operating surplus to the common and subordinated unitholders in an amount equal to the minimum distribution, the Partnership will distribute any additional available cash from operating surplus for that quarter among the unitholders and the incentive distribution rights holders in the following manner: Marginal Percentage Interest in Distributions Total Quarterly Distribution Per Unit Unitholders IDR Holders Minimum Quarterly Distribution up to $0.3750 100 % — % First Target Distribution above $0.3750 up to $0.4313 100 % — % Second Target Distribution above $0.4313 up to $0.4688 85 % 15 % Third Target Distribution above $0.4688 up to $0.5625 75 % 25 % Thereafter above $0.5625 50 % 50 %

Earnings Per Limited Partner Un

Earnings Per Limited Partner Unit	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Limited Partner Unit	Earnings Per Limited Partner Unit Earnings per limited partner unit is computed by dividing the respective limited partners’ interest in earnings attributable to the Partnership by the weighted average number of common and subordinated units outstanding. Because there is more than one class of participating securities, the Partnership uses the two-class method when calculating earnings per limited partner unit. The classes of participating securities include common units, subordinated units, and incentive distribution rights. Diluted earnings per limited partner unit reflects the potential dilution that could occur if securities or agreements to issue common units, such as awards under the LTIP, were exercised, settled or converted into common units. When it is determined that potential common units should be included in diluted net income per limited partner unit calculation, the impact is reflected by applying the treasury stock method. The following table presents the calculation of earnings per limited partner unit for common and subordinated limited partner units: Year Ended December 31, 2017 (in thousands, except per unit data) Net income attributable to Oasis Midstream Partners LP $ 11,638 Less: Net income attributable to IDRs — Net income attributable to limited partners $ 11,638 Net income allocable to Common Units $ 5,819 Net income allocable to Subordinated Units 5,819 Net income attributable to limited partners $ 11,638 Net income attributable to limited partners per limited partner unit — Basic and Diluted Common Units $ 0.43 Subordinated Units 0.42 Weighted average limited partner units outstanding — Basic Common Units 13,566 Subordinated Units 13,750 Weighted average limited partner units outstanding — Diluted Common Units 13,568 Subordinated Units 13,750 Antidilutive restricted units 10

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events The Partnership has evaluated the period after the balance sheet date and through February 28, 2018, noting no subsequent events or transactions that required recognition or disclosure in the consolidated financial statements, other than as previously disclosed.

Quarterly Financial Data - Unau

Quarterly Financial Data - Unaudited	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data - Unaudited	Quarterly Financial Data - Unaudited The Partnership’s results of operations by quarter for the years ended December 31, 2017 and 2016 are as follows: Year ended December 31, 2017 First Quarter Second Quarter Third Quarter Fourth Quarter Revenues $ 37,640 $ 40,312 $ 47,381 $ 56,883 Operating income 20,763 23,102 25,135 33,363 Income before income taxes 19,544 20,089 22,407 33,365 Net income 12,249 12,424 14,509 33,365 Net income attributable to Oasis Midstream Partners LP (1) (1) 526 11,112 Earnings per limited partner unit - Basic and Diluted Common units (1) (1) 0.02 0.41 Subordinated units (1) (1) 0.02 0.40 (1) Information is not applicable for the periods prior to the Offering on September 25, 2017. Year ended December 31, 2016 First Quarter Second Quarter Third Quarter Fourth Quarter Revenues $ 29,818 $ 28,935 $ 29,277 $ 32,822 Operating income 17,575 17,699 16,525 19,141 Income before income taxes 17,087 16,364 13,937 17,597 Net income 10,434 10,235 8,493 10,966

Summary of Significant Accoun20

Summary of Significant Accounting Policies and Basis of Presentation (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements of the Partnership include the accounts of Oasis Midstream Partners LP and its subsidiaries. All significant intercompany transactions have been eliminated in consolidation. These statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”).
Use of Estimates	Use of Estimates Preparation of the Partnership’s consolidated financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ significantly from those estimates. Management evaluates estimates and assumptions on an ongoing basis using historical experience and other factors, including the current economic and commodity price environment.
Consolidation	Consolidation The Partnership’s consolidated financial statements include its accounts and the accounts of the DevCos, each of which is controlled by the general partner of the Partnership. All intercompany balances and transactions have been eliminated upon consolidation. Variable interest entities. With respect to Bobcat DevCo and Beartooth DevCo, management has determined that OMS’s equity at risk was established with non-substantive voting rights, making Bobcat DevCo and Beartooth DevCo variable interest entities (“VIEs”) under the rules of the Financial Accounting Standards Board (“FASB”). Through its 100% ownership interest in OMP Operating LLC (“OMP Operating”), which owns controlling interests in Bobcat DevCo and Beartooth DevCo, the Partnership has the authority to direct the activities that most significantly affect the economic performance of these entities and the obligation to absorb losses or the right to receive benefits that could be potentially significant to them. Therefore, the Partnership is considered the primary beneficiary of Bobcat DevCo and Beartooth DevCo and is required to consolidate these entities in its financial statements under the VIE consolidation model. The Partnership has determined that Bighorn DevCo is not a VIE due to OMP Operating’s 100% ownership interest in Bighorn DevCo, which is proportional to its voting rights through its controlling interest. The Partnership has a controlling financial interest in Bighorn DevCo, through its 100% ownership interest in OMP Operating, and is required to consolidate Bighorn DevCo in its financial statements under the voting interest consolidation model.
Non-controlling Interests	Non-controlling interests. The non-controlling interests represent Oasis Petroleum’s retained ownership interest in Bobcat DevCo and Beartooth DevCo of 90% and 60% , respectively.
Revenue Recognition	Revenue recognition. The Partnership generates revenue primarily by charging fees for midstream services for (i) crude oil gathering, stabilization, blending, storage and transportation, (ii) natural gas gathering, gas lift, compression and processing, (iii) produced and flowback water gathering and disposal and (iv) freshwater supply and distribution. The Partnership recognizes revenue when services have been rendered, the prices are fixed or determinable, and collectability is reasonable assured.
Cash and Cash Equivalents	Cash and cash equivalents. The Partnership classifies all unrestricted cash on hand and investments with original maturity dates less than 90 days as cash equivalents.
Transactions with Affiliates	Transactions with affiliates. Transactions between Oasis Petroleum, its affiliates and the Partnership have been identified in the consolidated financial statements as transactions with affiliates. See Note 3 . Transactions with Affiliates .
Property, Plant and Equipment	Property, plant and equipment. Property, plant and equipment consists primarily of pipelines, Gas Plant I, produced and flowback water facilities and compressor stations. Property, plant and equipment is stated at the lower of historical cost less accumulated depreciation, or fair value, if impaired. The Partnership capitalizes a portion of its interest expense incurred on its outstanding debt. The amount capitalized is determined by multiplying the capitalization rate by the average amount of eligible accumulated capital expenditures and is limited to actual interest costs incurred during the period. The accumulated capital expenditures included in the capitalized interest calculation begin when the first costs are incurred and end when the asset is either placed into production or written off. The Partnership capitalized $1.2 million , $4.4 million and $2.9 million of interest costs for the years ended December 31, 2017 , 2016 and 2015 , respectively. These amounts are amortized over the useful life of the related assets once the assets are placed in-service. When assets are placed into service, management makes estimates with respect to useful lives and salvage values that management believes are reasonable. However, subsequent events could cause a change in estimates, thereby impacting future depreciation amounts. Uncertainties that may impact these estimates include, among others, changes in laws and regulations relating to environmental matters, including air and water quality, restoration and abandonment requirements, economic conditions and supply and demand in the area. Depreciation is computed over the asset’s estimated useful life using the straight line method based on estimated useful lives and asset salvage values. The weighted average life of each of our pipelines, natural gas processing plant, produced and flowback water facilities, compressor stations, and other long-lived assets is 30 years. When properties are retired or otherwise disposed of, the related cost and accumulated depreciation are removed from the respective accounts and any profit or loss on disposition is recognized as gain or loss.
Impairment of Long-Lived Assets	Impairment of long-lived assets. The Partnership evaluates the ability to recover the carrying amount of long-lived assets and determine whether such long-lived assets have been impaired. Impairment exists when the carrying amount of an asset exceeds estimates of the undiscounted cash flows expected to result from the use and eventual disposition of the asset. An impairment analysis requires management to apply judgment in identifying impairment indicators and estimating future cash flows. When alternative courses of action to recover the carrying amount of a long-lived asset are under consideration, estimates of future undiscounted cash flows take into account possible outcomes and probabilities of their occurrence. If the carrying amount of the long-lived asset is not recoverable based on the estimated future undiscounted cash flows, the impairment loss is measured as the excess of the asset’s carrying amount over its estimated fair value, such that the asset’s carrying amount is adjusted to its estimated fair value with an offsetting charge to impairment expense. Fair value represents the estimated price between market participants to sell an asset in the principal or most advantageous market for the asset, based on assumptions a market participant would make. When warranted, management assesses the fair value of long-lived assets using commonly accepted techniques and may use more than one source in making such assessments. The factors used to determine fair value are subject to management’s judgment and expertise and include, but are not limited to, recent third-party comparable sales, internally developed discounted cash flow analysis and analysis from outside advisors. Significant changes, such as changes in contract rates or terms, the condition of an asset or management’s intent to utilize the asset, generally require management to reassess the cash flows related to long-lived assets. A reduction of the carrying value of fixed assets would represent a Level 3 fair value measurement. If actual results are not consistent with our assumptions and estimates or our assumptions and estimates change due to new information, we may be exposed to additional impairment charges. Ultimately, a prolonged period of lower commodity prices may adversely affect the estimate of future operating results through lower throughput volumes on the Partnership’s assets, which could result in future impairment charges due to the potential impact on operations and cash flows.
Asset Retirement Obligations	Asset retirement obligations (“ARO”). The Partnership records the fair value of a liability for a legal obligation to retire an asset in the period in which the liability is incurred, with the corresponding cost capitalized by increasing the carrying amount of the related long-lived asset. For produced and flowback water disposal wells, this is the period in which the well is drilled or acquired. The ARO represents the estimated amount we will incur to plug, abandon and remediate the produced and flowback water properties at the end of their useful lives, in accordance with applicable state laws. The liability is accreted to its present value each period and the capitalized costs are depreciated using the straight-line method. The accretion expense is recorded as a component of depreciation and amortization in the Consolidated Statements of Operations. Some assets, including certain pipelines and the natural gas processing plant, have contractual or regulatory obligations to perform remediation and, in some instances, dismantlement and removal activities when the assets are abandoned. The Partnership is not able to reasonably estimate the fair value of the ARO for these assets because the settlement dates are indeterminable given the expected continued use of the assets with proper maintenance. The Partnership will record an ARO for these assets in the periods in which the settlement dates become reasonably determinable. The Partnership determines the ARO, which represents a non-financial liability which is measured at fair value on a non-recurring basis, by calculating the present value of estimated cash flows related to the liability. Estimating the future ARO requires management to make estimates and judgments regarding timing and existence of a liability, as well as what constitutes adequate restoration. Inherent in the fair value calculation are numerous assumptions and judgments including the ultimate costs, inflation factors, credit adjusted discount rates, timing of settlement and changes in the legal, regulatory, environmental and political environments. These assumptions represent Level 3 inputs. To the extent future revisions to these assumptions impact the fair value of the existing ARO liability, a corresponding adjustment is made to the related asset.
Deferred Financing Costs	Deferred financing costs. The Partnership capitalizes directly attributable costs incurred in connection with obtaining debt financing. These costs are amortized over the term of the related financing using the straight-line method, which approximates the interest method. The amortization expense is recorded as a component of interest expense in the Partnership’s Consolidated Statements of Operations. The deferred financing costs related to the Partnership’s Revolving Credit Facility are included in other assets on the Partnership’s Consolidated Balance Sheets.
Unit-based Compensation	Unit-based compensation. The Partnership has granted phantom unit awards and restricted unit awards under the Oasis Midstream Partners LP 2017 Long Term Incentive Plan (“LTIP”). The Partnership accounts for phantom unit awards as liability-classified awards in accordance with GAAP, since the Partnership intends to settle these awards in cash. The Partnership will be reimbursed by Oasis Petroleum for the cash settlement amount of these awards. The Partnership accounts for restricted units granted to certain directors of the Partnership as equity-classified awards in accordance with GAAP, as the Partnership intends to settle these awards in common units.
Income Taxes	Income taxes. For the period subsequent to the Offering, the consolidated financial statements do not include a provision for income taxes as the Partnership is generally not subject to federal or state income tax. Generally, each partner is separately taxed on its share of taxable income. For periods prior to the Offering, the consolidated financial statements include a provision for income tax expense. Deferred federal and state income taxes were provided on temporary differences between the financial statement carrying amounts of recognized assets and liabilities and their respective tax bases as if the Partnership filed tax returns as a stand-alone entity.
Business Combinations	Business combinations. The Partnership accounts for business combinations under the acquisition method of accounting. An income, market or cost valuation method may be utilized to estimate the fair value of the assets acquired, liabilities assumed, and non-controlling interest, if any, in a business combination. Fair value is determined on the acquisition date. Acquisition-related costs are expensed as incurred in connection with each business combination. If the initial accounting for the business combination is incomplete by the end of the reporting period in which the acquisition occurs, an estimate will be recorded. Subsequent to the acquisition, and not later than one year from the acquisition date, the Partnership will record any material adjustments to the initial estimate based on new information obtained about facts and circumstances that existed as of the acquisition date. The Partnership makes various assumptions in estimating the fair values of assets acquired and liabilities assumed. As fair value is a market-based measurement, it is determined based on the assumptions that market participants would use. The income valuation method represents the present value of future cash flows over the life of the asset using discrete financial forecasts. Such discrete financial forecasts rely on estimates and assumptions made by management. The most significant assumptions relate to management’s estimates of throughput volumes, future operating and development costs, long-term growth rates and a market-based weighted average cost of capital. The market valuation method uses prices paid for a reasonably similar asset by other purchasers in the market, with adjustments relating to any differences between the assets. The cost valuation method is based on the replacement cost of a comparable asset at prices at the time of the acquisition reduced for depreciation of the asset. Any excess of the acquisition price over the estimated fair value of net assets acquired is recorded as goodwill. Any excess of the estimated fair value of net assets acquired over the acquisition price is recorded in current earnings as a gain on bargain purchase.
Concentrations of Credit Risk	Concentrations of Market and Credit Risk The Partnership has limited direct exposure to risks associated with fluctuating commodity prices due to the nature of its business and its long-term, fixed-fee arrangements with Oasis Petroleum. However, to the extent that the future contractual arrangements with Oasis Petroleum or third parties do not provide for fixed-fee structures, the Partnership may become subject to commodity price risk.
Concentrations of Market	Additionally, as substantially all of the Partnership’s revenues are derived from Oasis Petroleum, the Partnership is indirectly subject to risks associated with fluctuating commodity prices to the extent that lower commodity prices adversely affect Oasis Petroleum’s production, drilling schedule, financial condition, leverage, market reputation, liquidity, results of operations or cash flows.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Revenue Recognition In May 2014, the FASB issued Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (“ASU 2014-09”). The objective of ASU 2014-09 is greater consistency and comparability across industries by using a five-step model to recognize revenue from customer contracts. ASU 2014-09 also contains enhanced disclosure requirements under GAAP. In August 2015, the FASB issued Accounting Standards Update No. 2015-14, Deferral of the Effective Date (“ASU 2015-14”). ASU 2015-14 defers the effective date of the new revenue standard by one year, making it effective for annual reporting periods beginning after December 15, 2017, including interim periods within that reporting period. In 2016 and 2017, the FASB issued additional accounting standards updates to clarify the implementation guidance of ASU 2014-09. During 2017, the Partnership completed its analysis of the impact of the standard on its contract types comprising each of its significant revenue streams, and it does not believe that the adoption of ASU 2014-09 has a material impact on its financial position, cash flows and results of operations but could impact certain disclosures. The Partnership has also modified current processes and controls to apply the requirements of the new standard and does not believe such modifications are material to its internal controls over financial reporting. Leases In February 2016, the FASB issued Accounting Standards Update No. 2016-02, Leases (“ASU 2016-02”), which requires a lessee to recognize lease payment obligations and a corresponding right-of-use asset to be measured at fair value on the balance sheet. ASU 2016-02 also requires certain qualitative and quantitative disclosures about the amount, timing and uncertainty of cash flows arising from leases. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018, including interim periods within those years. Also, in January 2018, the FASB issued Accounting Standards Update No. 2018-01, Land easement practical expedient for transition to Topic 842 (“ASU 2018-01”), which provides an optional transition practical expedient to not evaluate under Topic 842 existing or expired land easements that were not previously accounted for as leases under Topic 840, Leases. The Partnership plans to elect this practical expedient and is currently evaluating the effect that adopting the new lease guidance will have on its financial position, cash flows and results of operations. Statement of Cash Flows In August 2016, the FASB issued Accounting Standards Update No. 2016-15, Statement of Cash Flows (“ASU 2016-15”), which is intended to reduce diversity in practice in how certain transactions are classified in the statement of cash flows. ASU 2016-15 is effective for fiscal years beginning after December 15, 2017, including interim periods within those years, and is required to be applied under the retrospective method. The Partnership will adopt the new standard on the effective date of January 1, 2018. The Partnership does not expect the adoption of this guidance to have a material impact on its financial position, cash flows or results of operations. Income Taxes In October 2016, the FASB issued Accounting Standards Update No. 2016-16, Intra-Entity Transfers of Assets Other Than Inventory (“ASU 2016-16”), to improve the accounting for the income tax consequences of intra-entity transfers of assets other than inventory. ASU 2016-16 is effective for fiscal years beginning after December 15, 2017, including interim periods within those years, and is required to be applied on a modified retrospective basis. The Partnership will adopt the new standard on the effective date of January 1, 2018. The Partnership does not expect the adoption of this guidance to have a material impact on its financial position, cash flows or results of operations. Business Combinations In January 2017, the FASB issued Accounting Standards Update No. 2017-01, Clarifying the Definition of a Business (“ASU 2017-01”), which provides guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. ASU 2017-01 requires entities to use a screen test to determine when an integrated set of assets and activities is not a business or if the integrated set of assets and activities needs to be further evaluated against the framework. ASU 2017-01 is effective for fiscal years beginning after December 15, 2017, including interim periods within those years, and is required to be applied prospectively. The Partnership will adopt the new standard on the effective date of January 1, 2018. The Partnership does not expect the adoption of this guidance to have a material impact on its financial position, cash flows or results of operations. Equity-Based Compensation In May 2017, the FASB issued Accounting Standards Update No. 2017-09, Scope of Modification Accounting (“ASU 2017-09”), which provides guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting. ASU 2017-09 is effective for annual periods beginning after December 15, 2017, including interim periods within those years, and is required to be applied prospectively. The Partnership will adopt the new standard on the effective date of January 1, 2018. The Partnership does not expect the adoption of this guidance to have a material impact on its financial position, cash flows or results of operations.

Organization and Nature of Op21

Organization and Nature of Operations (Tables)	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Ownership Interests in DevCos	In connection with the Offering, Oasis Petroleum contributed to the Partnership ownership interests in the following DevCos: DevCos Areas Served Service Lines Oasis Midstream Ownership Bighorn DevCo Wild Basin – Gas processing – Crude stabilization – Crude blending – Crude storage – Crude transportation 100% Bobcat DevCo Wild Basin – Gas gathering – Gas compression – Gas lift – Crude gathering – Produced and flowback water gathering – Produced and flowback water disposal 10% Beartooth DevCo Alger – Produced and flowback water gathering – Produced and flowback water disposal – Freshwater supply and distribution 40%

Transactions with Affiliates (T

Transactions with Affiliates (Tables)	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Schedule of Related Party Operating Expenses	Operating expenses incurred from transactions with Oasis Petroleum are shown below for the periods presented: Year Ended December 31, 2017 2016 2015 Operating expenses (1) General and administrative $ 12,828 $ 7,821 $ 6,140 Interest expense, net of capitalized interest 6,945 5,481 4,514 ___________________ (1) Transactions between the Predecessor and Oasis Petroleum are shown above for the periods prior to the Offering on September 25, 2017 .

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Schedule of Accrued Liabilities	Accrued liabilities consist of the following: December 31, 2017 December 31, 2016 (In thousands) Accrued capital costs $ 47,843 $ 27,085 Accrued operating expenses 10,860 3,913 Other accrued liabilities 115 1,181 Total accrued liabilities (1) $ 58,818 $ 32,179 ___________________ (1) Accrued liabilities as of December 31, 2017 represent the obligations of the Partnership subsequent to the Offering, while accrued liabilities as of December 31, 2016 represent the obligations of the Predecessor.

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Schedule of Property, Plant and Equipment	Property, plant and equipment consists of the following: December 31, 2017 December 31, 2016 (In thousands) Pipelines $ 255,231 $ 199,943 Natural gas processing plant 102,371 92,630 Produced and flowback water facilities 80,050 75,828 Compressor stations 59,293 35,507 Other property and equipment 32,340 31,039 Construction in progress 124,643 18,748 Total property, plant and equipment 653,928 453,695 Less: accumulated depreciation and amortization (34,348 ) (22,160 ) Total property, plant and equipment, net $ 619,580 $ 431,535

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of Applicable Debt Margins	As of December 31, 2017 , any outstanding ABR or Eurodollar loans would have borne their respective interest rates plus the applicable margin indicated in the following table: Consolidated Total Leverage Ratio Applicable Margin for Eurodollar Loans Applicable Margin for ABR Loans Commitment Fee Rate Less than or equal to 3.00 to 1.00 1.75 % 0.75 % 0.375 % Greater than 3.00 to 1.00 but less than or equal to 3.50 to 1.00 2.00 % 1.00 % 0.375 % Greater than 3.50 to 1.00 but less than or equal to 4.00 to 1.00 2.25 % 1.25 % 0.500 % Greater than 4.00 to 1.00 but less than or equal to 4.50 to 1.00 2.50 % 1.50 % 0.500 % Greater than 4.50 to 1.00 2.75 % 1.75 % 0.500 %

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	The Predecessor’s income tax expense consists of the following: December 31, 2017 2016 2015 Current: Federal $ 15,571 $ 21,272 $ 14,811 State 2,047 2,797 1,985 17,618 24,069 16,796 Deferred: Federal 4,631 772 3,191 State 609 16 352 5,240 788 3,543 Total income tax expense $ 22,858 $ 24,857 $ 20,339
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	The reconciliation of income taxes calculated at the U.S. federal statutory rate to the Predecessor’s effective tax rate for the years presented is as follows: December 31, 2017 2016 2015 (%) (In thousands) (%) (In thousands) (%) (In thousands) U.S. federal statutory rate 35.00 % 33,392 35.00 % 22,745 35.00 % 18,648 Earnings not subject to tax subsequent to the Offering (12.83 )% (12,239 ) — % — — % — State income taxes, net of federal income tax benefit 1.81 % 1,727 2.90 % 1,882 2.94 % 1,565 Other (0.02 )% (22 ) 0.35 % 230 0.23 % 126 Annual effective tax rate 23.96 % 22,858 38.25 % 24,857 38.17 % 20,339

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments	Future minimum rental payments at December 31, 2017 are as follows: (In thousands) 2018 $ 4,372 2019 292 2020 — 2021 — 2022 — Thereafter — $ 4,664
Schedule of Future Minimum Commitments	Purchase commitments. The Partnership is party to certain contractual agreements to purchase a minimum quantity of freshwater. Future commitments at December 31, 2017 are as follows: (In thousands) 2018 $ 373 2019 400 2020 414 2021 1,200 2022 — Thereafter — $ 2,387

Equity-Based Compensation (Tabl

Equity-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Phantom Units Held by Certain Non-employees of the Partnership	The following table summarizes information related to Phantom Units held by certain non-employees of the Partnership: Phantom Units Weighted Average Grant Date Fair Value per Unit Outstanding at beginning of period — $ — Granted 101,500 16.40 Vested — — Forfeited (2,400 ) 16.40 Outstanding at end of period 99,100 $ 16.40
Schedule of Nonvested Share Activity	The following table summarizes information related to restricted units held by certain directors of the Partnership: Restricted Units Weighted Average Grant Date Fair Value per Unit Outstanding at beginning of period — $ — Granted 11,766 17.00 Vested — — Forfeited — — Outstanding at end of period 11,766 $ 17.00

Partnership Equity and Distri29

Partnership Equity and Distributions (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Schedule of Percentage Allocations of Available Cash from Operating Surplus	For any quarter in which the Partnership has distributed cash from operating surplus to the common and subordinated unitholders in an amount equal to the minimum distribution, the Partnership will distribute any additional available cash from operating surplus for that quarter among the unitholders and the incentive distribution rights holders in the following manner: Marginal Percentage Interest in Distributions Total Quarterly Distribution Per Unit Unitholders IDR Holders Minimum Quarterly Distribution up to $0.3750 100 % — % First Target Distribution above $0.3750 up to $0.4313 100 % — % Second Target Distribution above $0.4313 up to $0.4688 85 % 15 % Third Target Distribution above $0.4688 up to $0.5625 75 % 25 % Thereafter above $0.5625 50 % 50 %

Earnings Per Limited Partner 30

Earnings Per Limited Partner Unit (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Schedule of Earnings per Common and Subordinated Units	The following table presents the calculation of earnings per limited partner unit for common and subordinated limited partner units: Year Ended December 31, 2017 (in thousands, except per unit data) Net income attributable to Oasis Midstream Partners LP $ 11,638 Less: Net income attributable to IDRs — Net income attributable to limited partners $ 11,638 Net income allocable to Common Units $ 5,819 Net income allocable to Subordinated Units 5,819 Net income attributable to limited partners $ 11,638 Net income attributable to limited partners per limited partner unit — Basic and Diluted Common Units $ 0.43 Subordinated Units 0.42 Weighted average limited partner units outstanding — Basic Common Units 13,566 Subordinated Units 13,750 Weighted average limited partner units outstanding — Diluted Common Units 13,568 Subordinated Units 13,750 Antidilutive restricted units 10

Quarterly Financial Data - Un31

Quarterly Financial Data - Unaudited (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data - Unaudited	The Partnership’s results of operations by quarter for the years ended December 31, 2017 and 2016 are as follows: Year ended December 31, 2017 First Quarter Second Quarter Third Quarter Fourth Quarter Revenues $ 37,640 $ 40,312 $ 47,381 $ 56,883 Operating income 20,763 23,102 25,135 33,363 Income before income taxes 19,544 20,089 22,407 33,365 Net income 12,249 12,424 14,509 33,365 Net income attributable to Oasis Midstream Partners LP (1) (1) 526 11,112 Earnings per limited partner unit - Basic and Diluted Common units (1) (1) 0.02 0.41 Subordinated units (1) (1) 0.02 0.40 (1) Information is not applicable for the periods prior to the Offering on September 25, 2017. Year ended December 31, 2016 First Quarter Second Quarter Third Quarter Fourth Quarter Revenues $ 29,818 $ 28,935 $ 29,277 $ 32,822 Operating income 17,575 17,699 16,525 19,141 Income before income taxes 17,087 16,364 13,937 17,597 Net income 10,434 10,235 8,493 10,966

Organization and Nature of Op32

Organization and Nature of Operations (Details) $ / shares in Units, a in Thousands, $ in Thousands	Sep. 25, 2017$ / sharesshares	Dec. 31, 2017USD ($)a	Dec. 31, 2017aarea
Limited Partners' Capital Account [Line Items]
Number of primary areas with developed infrastructure | area			2
Common Units [Member]
Limited Partners' Capital Account [Line Items]
Common units sold in public offering (shares) | shares	7,500,000
Price of common units sold (in usd per share) | $ / shares	$ 17
Price of common units sold, net of underwriting discounts and commission (in usd per share) | $ / shares	$ 15.98
Net proceeds from the initial public offering | $		$ 134,185
Common Units [Member] | Over-Allotment Option [Member]
Limited Partners' Capital Account [Line Items]
Common units sold in public offering (shares) | shares	1,125,000
Bighorn DevCo [Member]
Limited Partners' Capital Account [Line Items]
Ownership interest (percent)			100.00%
Bobcat DevCo [Member]
Limited Partners' Capital Account [Line Items]
Ownership interest (percent)			10.00%
Beartooth DevCo [Member]
Limited Partners' Capital Account [Line Items]
Ownership interest (percent)			40.00%
Wild Basin [Member] | Oil, Gas and Water Services [Member]
Limited Partners' Capital Account [Line Items]
Gross dedicated acreage received from Oasis (acres)		65	65
Dedicated acreage still within Oasis' gross operated acreage position (acres)		29	29
Wild Basin [Member] | Produced Water [Member]
Limited Partners' Capital Account [Line Items]
Gross dedicated acreage received from Oasis (acres)		581	581
Dedicated acreage still within Oasis' gross operated acreage position (acres)		299	299
Wild Basin [Member] | Fresh Water [Member]
Limited Partners' Capital Account [Line Items]
Gross dedicated acreage received from Oasis (acres)		364	364
Dedicated acreage still within Oasis' gross operated acreage position (acres)		203	203
Oasis Petroleum [Member]
Limited Partners' Capital Account [Line Items]
Proceeds from the Offering distributed to Oasis Petroleum | $		$ 132,083
Oasis Petroleum [Member] | Common Units [Member]
Limited Partners' Capital Account [Line Items]
Common units sold in public offering (shares) | shares	5,125,000
Oasis Petroleum [Member] | Subordinated Units [Member]
Limited Partners' Capital Account [Line Items]
Common units sold in public offering (shares) | shares	13,750,000

Basis of Presentation (Details)

Basis of Presentation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Interest costs capitalized	$ 1.2	$ 4.4	$ 2.9
Weighted average useful life of long-lived assets	30 years
Bighorn DevCo [Member]
Variable Interest Entity [Line Items]
Ownership interest (percent)	100.00%
Bobcat DevCo [Member]
Variable Interest Entity [Line Items]
Ownership interest (percent)	10.00%
Beartooth DevCo [Member]
Variable Interest Entity [Line Items]
Ownership interest (percent)	40.00%
OMP Operating, LLC [Member] | Bighorn DevCo [Member]
Variable Interest Entity [Line Items]
Ownership interest (percent)	100.00%
Oasis Petroleum [Member] | Bobcat DevCo [Member]
Variable Interest Entity [Line Items]
Non-controlling interest (percent)	90.00%
Oasis Petroleum [Member] | Beartooth DevCo [Member]
Variable Interest Entity [Line Items]
Non-controlling interest (percent)	60.00%

Transactions with Affiliates (D

Transactions with Affiliates (Details) - Oasis [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
General and administrative	$ 12,828	$ 7,821	$ 6,140
Interest expense, net of capitalized interest	$ 6,945	$ 5,481	$ 4,514
Commercial Agreements with OPNA, Oasis Petroleum Marketing LLC (“OPM”) and OMS [Member]
Related Party Transaction [Line Items]
Term of contractual arrangements	15 years
Centralized Corporate, General and Administrative Services [Member] | Commercial Agreements with OPNA, Oasis Petroleum Marketing LLC (“OPM”) and OMS [Member]
Related Party Transaction [Line Items]
Term of contractual arrangements	15 years

Accrued Liabilities (Details)

Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Accrued capital costs	$ 47,843	$ 27,085
Accrued operating expenses	10,860	3,913
Other accrued liabilities	115	1,181
Total accrued liabilities	$ 58,818	$ 32,179

Property, Plant and Equipment36

Property, Plant and Equipment (Details) - USD ($)	Nov. 06, 2017	Apr. 25, 2017	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, plant and equipment			$ 653,928,000	$ 453,695,000
Less: accumulated depreciation and amortization			(34,348,000)	(22,160,000)
Total property, plant and equipment, net			619,580,000	431,535,000
MIdstream Assets in McKenzie County, North Dakota [Member]
Property, Plant and Equipment [Line Items]
Consideration transferred		$ 12,700,000
Installment notes payable		4,900,000
Estimated fair value of assets acquired		12,700,000
Goodwill		$ 0
Pipelines [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment			255,231,000	199,943,000
Natural Gas Processing Plant [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment			102,371,000	92,630,000
Produced and Flowback Water Facilities [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment			80,050,000	75,828,000
Compressor Stations [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment			59,293,000	35,507,000
Other Property and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment			32,340,000	31,039,000
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment			$ 124,643,000	$ 18,748,000
Gas Gathering, Compression, Processing and Gas Lift Agreement [Member] | Estimated Reimbursements, Plant II [Member] | Oasis [Member]
Property, Plant and Equipment [Line Items]
Related party reimbursement (percent)	100.00%
Related party transactions	$ 66,700,000

Long-Term Debt (Details)

Long-Term Debt (Details)	12 Months Ended
	Dec. 31, 2017USD ($)	Sep. 25, 2017USD ($)
Line of Credit Facility [Line Items]
Maximum consolidated senior secured leverage ratio	3.75
Covenant Period One [Member]
Line of Credit Facility [Line Items]
Maximum consolidated total leverage ratio	4.50
Minimum consolidated interest coverage ratio	3
Covenant Period Two [Member]
Line of Credit Facility [Line Items]
Maximum consolidated total leverage ratio	5
Minimum consolidated interest coverage ratio	2.50
Covenant Period Three [Member]
Line of Credit Facility [Line Items]
Maximum consolidated total leverage ratio	5.25
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Borrowing capacity increase limit		$ 400,000,000
Amounts outstanding under credit facility	$ 78,000,000
Minimum aggregate principal amount threshold under covenant	$ 150,000,000
ABR Loans [Member] | Revolving Credit Facility [Member] | Adjusted (LIBOR) Rate [Member]
Line of Credit Facility [Line Items]
Spread on variable rate (percent)	1.00%
Eurodollar Loans [Member] | Revolving Credit Facility [Member] | Adjusted (LIBOR) Rate [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Spread on variable rate (percent)	1.75%
Eurodollar Loans [Member] | Revolving Credit Facility [Member] | Adjusted (LIBOR) Rate [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Spread on variable rate (percent)	2.75%
ABR Loans or Swingline Loans [Member] | Revolving Credit Facility [Member] | Federal Funds Effective Rate [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Spread on variable rate (percent)	0.75%
ABR Loans or Swingline Loans [Member] | Revolving Credit Facility [Member] | Federal Funds Effective Rate [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Spread on variable rate (percent)	1.75%
ABR Loans or Swingline Loans [Member] | Revolving Credit Facility [Member] | Adjusted (LIBOR) Rate [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Spread on variable rate (percent)	0.75%
ABR Loans or Swingline Loans [Member] | Revolving Credit Facility [Member] | Adjusted (LIBOR) Rate [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Spread on variable rate (percent)	1.75%
The Credit Agreement [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Maximum aggregate commitment amount		200,000,000
The Credit Agreement [Member] | Letters of Credit [Member]
Line of Credit Facility [Line Items]
Maximum aggregate commitment amount		10,000,000
The Credit Agreement [Member] | Swingline Loans [Member]
Line of Credit Facility [Line Items]
Maximum aggregate commitment amount		$ 10,000,000

Long-Term Debt - Debt Marginal

Long-Term Debt - Debt Marginal Rates (Details)	12 Months Ended
	Dec. 31, 2017
Less than or equal to 3.00 to 1.00 [Member] | Maximum [Member]
Debt Instrument [Line Items]
Consolidated total leverage ratio	3
Greater than 3.00 to 1.00 but less than or equal to 3.50 to 1.00 [Member] | Minimum [Member]
Debt Instrument [Line Items]
Consolidated total leverage ratio	3
Greater than 3.00 to 1.00 but less than or equal to 3.50 to 1.00 [Member] | Maximum [Member]
Debt Instrument [Line Items]
Consolidated total leverage ratio	3.50
Greater than 3.50 to 1.00 but less than or equal to 4.00 to 1.00 [Member] | Minimum [Member]
Debt Instrument [Line Items]
Consolidated total leverage ratio	3.50
Greater than 3.50 to 1.00 but less than or equal to 4.00 to 1.00 [Member] | Maximum [Member]
Debt Instrument [Line Items]
Consolidated total leverage ratio	4
Greater than 4.00 to 1.00 but less than or equal to 4.50 to 1.00 [Member] | Minimum [Member]
Debt Instrument [Line Items]
Consolidated total leverage ratio	4
Greater than 4.00 to 1.00 but less than or equal to 4.50 to 1.00 [Member] | Maximum [Member]
Debt Instrument [Line Items]
Consolidated total leverage ratio	4.50
Greater than 4.50 to 1.00 [Member] | Minimum [Member]
Debt Instrument [Line Items]
Consolidated total leverage ratio	4.50
OMP Revolving Line of Credit [Member] | Less than or equal to 3.00 to 1.00 [Member]
Debt Instrument [Line Items]
Commitment fee rate (percent)	0.375%
OMP Revolving Line of Credit [Member] | Less than or equal to 3.00 to 1.00 [Member] | Eurodollar Loans [Member]
Debt Instrument [Line Items]
Applicable margin (percent)	1.75%
OMP Revolving Line of Credit [Member] | Less than or equal to 3.00 to 1.00 [Member] | Alternate Based Rate (ABR) [Member]
Debt Instrument [Line Items]
Applicable margin (percent)	0.75%
OMP Revolving Line of Credit [Member] | Greater than 3.00 to 1.00 but less than or equal to 3.50 to 1.00 [Member]
Debt Instrument [Line Items]
Commitment fee rate (percent)	0.375%
OMP Revolving Line of Credit [Member] | Greater than 3.00 to 1.00 but less than or equal to 3.50 to 1.00 [Member] | Eurodollar Loans [Member]
Debt Instrument [Line Items]
Applicable margin (percent)	2.00%
OMP Revolving Line of Credit [Member] | Greater than 3.00 to 1.00 but less than or equal to 3.50 to 1.00 [Member] | Alternate Based Rate (ABR) [Member]
Debt Instrument [Line Items]
Applicable margin (percent)	1.00%
OMP Revolving Line of Credit [Member] | Greater than 3.50 to 1.00 but less than or equal to 4.00 to 1.00 [Member]
Debt Instrument [Line Items]
Commitment fee rate (percent)	0.50%
OMP Revolving Line of Credit [Member] | Greater than 3.50 to 1.00 but less than or equal to 4.00 to 1.00 [Member] | Eurodollar Loans [Member]
Debt Instrument [Line Items]
Applicable margin (percent)	2.25%
OMP Revolving Line of Credit [Member] | Greater than 3.50 to 1.00 but less than or equal to 4.00 to 1.00 [Member] | Alternate Based Rate (ABR) [Member]
Debt Instrument [Line Items]
Applicable margin (percent)	1.25%
OMP Revolving Line of Credit [Member] | Greater than 4.00 to 1.00 but less than or equal to 4.50 to 1.00 [Member]
Debt Instrument [Line Items]
Commitment fee rate (percent)	0.50%
OMP Revolving Line of Credit [Member] | Greater than 4.00 to 1.00 but less than or equal to 4.50 to 1.00 [Member] | Eurodollar Loans [Member]
Debt Instrument [Line Items]
Applicable margin (percent)	2.50%
OMP Revolving Line of Credit [Member] | Greater than 4.00 to 1.00 but less than or equal to 4.50 to 1.00 [Member] | Alternate Based Rate (ABR) [Member]
Debt Instrument [Line Items]
Applicable margin (percent)	1.50%
OMP Revolving Line of Credit [Member] | Greater than 4.50 to 1.00 [Member]
Debt Instrument [Line Items]
Commitment fee rate (percent)	0.50%
OMP Revolving Line of Credit [Member] | Greater than 4.50 to 1.00 [Member] | Eurodollar Loans [Member]
Debt Instrument [Line Items]
Applicable margin (percent)	2.75%
OMP Revolving Line of Credit [Member] | Greater than 4.50 to 1.00 [Member] | Alternate Based Rate (ABR) [Member]
Debt Instrument [Line Items]
Applicable margin (percent)	1.75%

Income Taxes (Details)

Income Taxes (Details) $ in Thousands	3 Months Ended
	Dec. 31, 2017USD ($)
Income Tax Holiday [Line Items]
Predecessor net tax liabilities eliminated	$ 104,005
Difference between tax bases and reported amounts of Partnership's assets and liabilities	31,700
Predecessor [Member]
Income Tax Holiday [Line Items]
Predecessor net tax liabilities eliminated	$ 104,005

Income Taxes - Components of Pr

Income Taxes - Components of Predecessor's Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Federal, State and Local, Tax Expense (Benefit) [Abstract]
Deferred Income Tax Expense (Benefit)	$ 5,240	$ 788	$ 3,543
Total income tax expense	22,858	24,857	20,339
Predecessor [Member]
Current Federal, State and Local, Tax Expense (Benefit) [Abstract]
Federal	15,571	21,272	14,811
State	2,047	2,797	1,985
Current Income Tax Expense (Benefit)	17,618	24,069	16,796
Deferred Federal, State and Local, Tax Expense (Benefit) [Abstract]
Federal	4,631	772	3,191
State	609	16	352
Deferred Income Tax Expense (Benefit)	5,240	788	3,543
Total income tax expense	$ 22,858	$ 24,857	$ 20,339

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Effective Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
U.S. federal statutory rate (percent)	35.00%	35.00%	35.00%
Earnings not subject to tax subsequent to the Offering (percent)	(12.83%)	(0.00%)	(0.00%)
State income taxes, net of federal income tax benefit (percent)	1.81%	2.90%	2.94%
Other (percent)	(0.02%)	0.35%	0.23%
Annual effective tax rate (percent)	23.96%	38.25%	38.17%
U.S. federal statutory rate	$ 33,392	$ 22,745	$ 18,648
Earnings not subject to tax subsequent to the Offering	(12,239)	0	0
State income taxes, net of federal income tax benefit	1,727	1,882	1,565
Other	(22)	230	126
Total income tax expense	22,858	24,857	20,339
Predecessor [Member]
Income Tax Contingency [Line Items]
Total income tax expense	$ 22,858	$ 24,857	$ 20,339

Commitments and Contingencies42

Commitments and Contingencies (Details) - USD ($)	Mar. 23, 2017	Dec. 31, 2017
Loss Contingencies [Line Items]
Unrecorded commitments		$ 0
Rental expense		$ 1,800,000
Mirada Litigation
Loss Contingencies [Line Items]
Damages sought	$ 100,000,000

Commitments and Contingencies -

Commitments and Contingencies - Schedule of Future Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,018	$ 4,372
2,019	292
2,020	0
2,021	0
2,022	0
Thereafter	0
Future minimum rental payments	$ 4,664

Commitments and Contingencies44

Commitments and Contingencies - Schedule of Future Minimum Purchase Commitments (Details) $ in Thousands	Dec. 31, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,018	$ 373
2,019	400
2,020	414
2,021	1,200
2,022	0
Thereafter	0
Future commitments	$ 2,387

Equity-Based Compensation (Deta

Equity-Based Compensation (Details) - Long Term Incentive Plan (LTIP) [Member] - USD ($) $ / shares in Units, $ in Millions	Oct. 19, 2017	Sep. 25, 2017	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Sep. 25, 2017	Dec. 31, 2017	Dec. 31, 2015
Phantom Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted unit awards granted (shares)							101,500
Weighted average grant date per share (in dollars per share)							$ 16.40
Restricted Unit [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted unit awards granted (shares)		11,766					11,766
Weighted average grant date per share (in dollars per share)							$ 17
Predecessor [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of granted awards						3 years
Stock-based compensation expense				$ 1.1	$ 0.9			$ 0.7
Weighted average grant date per share (in dollars per share)							$ 14.95
Oasis Midstream Partners, LP [Member] | Phantom Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted unit awards granted (shares)	101,500
Aggregate number of common units that may be issued under LTIP (shares)	1,842,500
Vesting period of granted awards	3 years
Unrecognized compensation cost				1.6			$ 1.6
Expected recognition period							2 years 9 months 29 days
OMP General Partner LLC [Member] | Restricted Unit [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost				$ 0.1			$ 0.1
Expected recognition period							8 months 12 days
Vesting period			1 year
Stock-based compensation expense							$ 0.1

Equity-Based Compensation - Sch

Equity-Based Compensation - Schedule of Equity Units Activity (Details) - Long Term Incentive Plan (LTIP) [Member] - $ / shares	Sep. 25, 2017	Dec. 31, 2017
Phantom Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding at beginning of period (shares)		0
Granted (shares)		101,500
Vested (shares)		0
Forfeited (shares)		(2,400)
Outstanding at end of period (shares)		99,100
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted average grant date per share, outstanding (in dollars per share)		$ 0
Weighted average grant date per share, granted (in dollars per share)		16.40
Weighted average grant date per share, vested (in dollars per share)		0
Weighted average grant date per share, forfeited (in dollars per share)		16.40
Weighted average grant date per share, outstanding (in dollars per share)		$ 16.40
Restricted Unit [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding at beginning of period (shares)		0
Granted (shares)	11,766	11,766
Vested (shares)		0
Forfeited (shares)		0
Outstanding at end of period (shares)		11,766
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted average grant date per share, outstanding (in dollars per share)		$ 0
Weighted average grant date per share, granted (in dollars per share)		17
Weighted average grant date per share, vested (in dollars per share)		0
Weighted average grant date per share, forfeited (in dollars per share)		0
Weighted average grant date per share, outstanding (in dollars per share)		$ 17

Partnership Equity and Distri47

Partnership Equity and Distributions (Details) - Cash Distribution [Member] - $ / shares	Feb. 02, 2018	Dec. 31, 2017	Dec. 31, 2017
Distribution Made to Limited Partner [Line Items]
Partners periodic distribution (in dollars per share)		$ 0.3750	$ 1.50
Termination threshold as percentage of sum of minimum distribution multiplied by total number of units outstanding (percent)			150.00%
General Partners' maximum interest in excess cash distribution (percent)			50.00%
Basis for General Partners' interest in distributions (in dollars per share)			$ 0.43125
Target Distribution up to $0.375 [Member]
Distribution Made to Limited Partner [Line Items]
Partners periodic distribution (in dollars per share)			0.375
Target Distribution above $0.375 up to $0.4313 [Member] | Minimum [Member]
Distribution Made to Limited Partner [Line Items]
Partners periodic distribution (in dollars per share)			0.375
Target Distribution above $0.375 up to $0.4313 [Member] | Maximum [Member]
Distribution Made to Limited Partner [Line Items]
Partners periodic distribution (in dollars per share)			0.4313
Target Distribution above $0.4313 up to $0.4688 [Member] | Minimum [Member]
Distribution Made to Limited Partner [Line Items]
Partners periodic distribution (in dollars per share)			0.4313
Target Distribution above $0.4313 up to $0.4688 [Member] | Maximum [Member]
Distribution Made to Limited Partner [Line Items]
Partners periodic distribution (in dollars per share)			0.4688
Target Distribution above $$0.4688 up to 0.5625 [Member] | Minimum [Member]
Distribution Made to Limited Partner [Line Items]
Partners periodic distribution (in dollars per share)			0.4688
Target Distribution above $$0.4688 up to 0.5625 [Member] | Maximum [Member]
Distribution Made to Limited Partner [Line Items]
Partners periodic distribution (in dollars per share)			0.5625
Target Distribution above $0.5625 [Member] | Minimum [Member]
Distribution Made to Limited Partner [Line Items]
Partners periodic distribution (in dollars per share)			$ 0.5625
Unitholders [Member] | Target Distribution up to $0.375 [Member]
Distribution Made to Limited Partner [Line Items]
Marginal percentage interest in distributions (percent)		100.00%	100.00%
Unitholders [Member] | Target Distribution above $0.375 up to $0.4313 [Member]
Distribution Made to Limited Partner [Line Items]
Marginal percentage interest in distributions (percent)		100.00%	100.00%
Unitholders [Member] | Target Distribution above $0.4313 up to $0.4688 [Member]
Distribution Made to Limited Partner [Line Items]
Marginal percentage interest in distributions (percent)		85.00%	85.00%
Unitholders [Member] | Target Distribution above $$0.4688 up to 0.5625 [Member]
Distribution Made to Limited Partner [Line Items]
Marginal percentage interest in distributions (percent)		75.00%	75.00%
Unitholders [Member] | Target Distribution above $0.5625 [Member]
Distribution Made to Limited Partner [Line Items]
Marginal percentage interest in distributions (percent)		50.00%	50.00%
IDR holders [Member] | Target Distribution up to $0.375 [Member]
Distribution Made to Limited Partner [Line Items]
Marginal percentage interest in distributions (percent)		0.00%	0.00%
IDR holders [Member] | Target Distribution above $0.375 up to $0.4313 [Member]
Distribution Made to Limited Partner [Line Items]
Marginal percentage interest in distributions (percent)		0.00%	0.00%
IDR holders [Member] | Target Distribution above $0.4313 up to $0.4688 [Member]
Distribution Made to Limited Partner [Line Items]
Marginal percentage interest in distributions (percent)		15.00%	15.00%
IDR holders [Member] | Target Distribution above $$0.4688 up to 0.5625 [Member]
Distribution Made to Limited Partner [Line Items]
Marginal percentage interest in distributions (percent)		25.00%	25.00%
IDR holders [Member] | Target Distribution above $0.5625 [Member]
Distribution Made to Limited Partner [Line Items]
Marginal percentage interest in distributions (percent)		50.00%	50.00%
Subsequent Event [Member]
Distribution Made to Limited Partner [Line Items]
Quarterly cash distribution paid (in usd per share)	$ 0.375
Quarterly cash distribution declared (in usd per share	$ 0.0245

Earnings Per Limited Partner 48

Earnings Per Limited Partner Unit (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended			12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2017
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 11,112	$ 11,638	$ 526	$ 11,638
Restricted Unit [Member]
Weighted average limited partner units outstanding — Diluted
Antidilutive restricted units (in shares)				10
Common Units [Member]
Net income attributable to limited partners per limited partner unit — Basic and Diluted
Basic and Diluted (in usd per share)	$ 0.41	$ 0.43	$ 0.02	$ 0.43
Weighted average limited partner units outstanding — Basic
Weighted average number of limited partner units outstanding (Basic) (shares)				13,566
Weighted average limited partner units outstanding — Diluted
Weighted average number of limited partner units outstanding (Diluted) (shares)				13,568
Subordinated Units [Member]
Net income attributable to limited partners per limited partner unit — Basic and Diluted
Basic and Diluted (in usd per share)	$ 0.40	$ 0.42	$ 0.02	$ 0.42
Weighted average limited partner units outstanding — Basic
Weighted average number of limited partner units outstanding (Basic) (shares)				13,750
Weighted average limited partner units outstanding — Diluted
Weighted average number of limited partner units outstanding (Diluted) (shares)				13,750
Public [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income				$ 0
Unitholders [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income				11,638
Unitholders [Member] | Common Units [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income				5,819
Unitholders [Member] | Subordinated Units [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income				$ 5,819

Quarterly Financial Data - Un49

Quarterly Financial Data - Unaudited (Details) - USD ($) $ in Thousands	3 Months Ended									9 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 25, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Revenues	$ 56,883		$ 47,381	$ 40,312	$ 37,640	$ 32,822	$ 29,277	$ 28,935	$ 29,818		$ 182,216	$ 120,852	$ 104,696
Operating income	33,363		25,135	23,102	20,763	19,141	16,525	17,699	17,575		102,363	70,940	58,095
Income before income taxes	33,365		22,407	20,089	19,544	17,597	13,937	16,364	17,087		95,405	64,985	52,781
Net income	33,365	$ 34,970	14,509	$ 12,424	$ 12,249	$ 10,966	$ 8,493	$ 10,235	$ 10,434	$ 37,577	72,547	$ 40,128	$ 32,442
Net income attributable to Oasis Midstream Partners LP	$ 11,112	$ 11,638	$ 526								$ 11,638