Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, smaller reporting company or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Energen Corporation (Energen or the Company) is an oil and natural gas exploration and production company engaged in the exploration, development and production of oil, natural gas liquids and natural gas. Our operations are conducted through our subsidiary, Energen Resources Corporation (Energen Resources) and primarily occur within the Midland Basin, the Delaware Basin and the Central Basin Platform areas of the Permian Basin in west Texas and New Mexico. Our corporate headquarters are located in Birmingham, Alabama. The unaudited consolidated financial statements and notes should be read in conjunction with the financial statements and notes thereto included in the 2016 Annual Report of Energen on Form 10-K.

Our accompanying unaudited consolidated financial statements include Energen and its subsidiaries, principally Energen Resources, and have been prepared in accordance with accounting principles generally accepted in the United States of America for interim financial information and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the disclosures required for complete financial statements. Results of operations for interim periods are not necessarily indicative of the results that may be expected for the year. In the opinion of management, the accompanying financial statements reflect all adjustments necessary to present a fair statement of our financial position, results of operations, and cash flows for the periods and as of the dates shown. Such adjustments consist of normal recurring items. Certain reclassifications were made to conform prior periods’ financial statements to the current-quarter presentation.

On January 22, 2016 and March 18, 2016, we reduced our workforce as part of an overall plan to reduce costs and better align our workforce with the needs of our business. In connection with the reductions, we incurred charges of approximately $5.0 million during 2016 for one-time termination benefits which are included in general and administrative expense on the consolidated statements of operations.

We periodically enter into derivative commodity instruments to hedge our exposure to price fluctuations on oil, natural gas liquids and natural gas production. These derivative commodity instruments are accounted for as mark-to-market transactions with gains or losses recognized in the period of change in gain (loss) on derivative instruments, net. Such instruments may include over-the-counter (OTC) swaps, options and basis swaps typically executed with investment and commercial banks and energy-trading firms. Derivative transactions are pursuant to standing authorizations by the Board of Directors, which do not authorize speculative positions.

The following tables detail the offsetting of derivative assets and liabilities as well as the fair values of derivatives on the balance sheets:

Due to the volatility of commodity prices, the estimated fair value of our derivative instruments is subject to fluctuation from period to period, which could result in significant differences between the current estimated fair value and the ultimate settlement price. Additionally, Energen is at risk of economic loss based upon the creditworthiness of our counterparties. We were in a net gainloss position

with thirteennine of our active counterparties and in a net lossgain position with the remaining onefive at JuneSeptember 30, 2017. The three largest counterparty net gain positions at JuneSeptember 30, 2017, PNC Bank, National Association, J.P. Morgan VenturesRegions Bank and NextEra Energy Corporation and J Aron and Company,Power Marketing, LLC, constituted approximately $6.4$1.9 million, $6.0$1.1 million and $5.1$1.0 million, respectively, of Energen’s total net gainloss on fair value of derivatives.

The following table details the effect of open and closed derivative commodity instruments not designated as hedging instruments on the statements of operations:

Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (exit price). In determining fair value, we use various valuation approaches and classify all assets and liabilities based on the lowest level of input that is significant to the fair value measurement. Observable inputs represent market data obtained from independent sources, whereas unobservable inputs reflect our own considerations about the assumptions other market participants would use in pricing the asset or liability based on the best information available in the circumstances. Assessing the significance of a particular input may require judgment considering factors specific to the asset or liability, and may affect the valuation of the asset or liability and its placement within the fair value hierarchy. The hierarchy is broken down into three levels based on the observability of inputs as follows:

  

Energen classifies the fair value of multiple derivative instruments executed under master netting arrangements as net derivative assets and liabilities. The following fair value hierarchy tables present information about Energen’s assets and liabilities measured at fair value on a recurring basis:

The table below sets forth a summary of changes in the fair value of Energen’s Level 3 derivative commodity instruments as follows:

*Includes $3.1$23.0 million and $11.0$14.2 million in gainslosses related to open contracts held at the reporting date for the three months and sixnine months ended JuneSeptember 30, 2017, respectively. Includes $3.7$1.5 million in gains and $6.1$1.6 million in losses for the three months and sixnine months ended JuneSeptember 30, 2016, respectively.

The table below sets forth quantitative information about Energen’s Level 3 fair value measurements of derivative commodity instruments as follows:

Certain assets and liabilities are reported at fair value on a nonrecurring basis in Energen’s consolidated balance sheets. The following methods and assumptions were used to estimate the fair values.values of these assets and liabilities.

The stated value of cash and cash equivalents, short-term investments, accounts receivable (net of allowance)allowance for doubtful accounts), and short-term debt approximates fair value due to the short maturity of the instruments. The Company invested in certain short-term investments that qualify and were classified as cash and cash equivalents. Energen had an allowance for doubtful accounts of $0.6$0.7 million at both JuneSeptember 30, 2017 and December 31, 2016, respectively. The fair value of Energen’s long-term debt, including the current portion, was approximately $690.5$779.6 million and $559.9 million and had a carrying value of $678.5$768.0 million and $554.0 million at JuneSeptember 30, 2017 and December 31, 2016, respectively. The fair values are based on market prices of similar debt issues having the same remaining maturities, redemption terms and credit rating. Short-term debt is classified as a Level 1 fair value measurement and long-term debt is classified as a Level 2 fair value measurement.

Long-term debt consisted of the following:

The aggregate maturities of Energen’s long-term debt outstanding at JuneSeptember 30, 2017 are as follows:

On January 23, 2017, Energen redeemed the $2.0 million of 7.40% Medium-term Notes, Series A, due July 24, 2017 and $5.0 million of 7.60% Medium-term Notes, Series A, due July 26, 2027. The Company also had $17.0 million of scheduled reductions in long-term debt in July 2017.

The debt agreements of Energen contain financial and nonfinancial covenants including routine matters such as timely payment of principal and interest, maintenance of corporate existence and restrictions on liens. Although none of the debt agreements have events of default based on credit ratings, the interest rates applicable to the syndicated credit facility discussed below may adjust based on credit rating changes during certain periods.

Under Energen’s Indenture dated September 1, 1996 with The Bank of New York as Trustee, a cross default provision provides that any debt default of more than $10 million by Energen or Energen Resources will constitute an event of default by Energen. The Indenture does not include a restriction on the payment of dividends.

income taxes, depreciation, depletion, amortization, exploration expense and other non-cash income and expenses (EBITDAX) less than or equal to 4.0 to 1.0; to maintain a ratio of consolidated current assets (adjusted to include amounts available for borrowings and exclude non-cash derivative instruments) to consolidated current liabilities (adjusted to exclude maturities under the credit facility and non-cash derivative instruments) greater than or equal to 1.0 to 1.0; and, during certain periods, to maintain a ratio of the net present value of proved reserves of our oil and natural gas properties to consolidated total debt greater than or equal to 1.50 to 1.0. We are also bound by covenants which limit our ability to incur additional indebtedness, make certain distributions or alter our corporate structure. Energen may not pay dividends duringif an event of default exists if the payment would result in an event of default, or if availability is less than 10 percent of the loan limit under the credit facility. Our credit facility also limits our ability to enter into commodity hedges based on projected production volumes. In addition, the terms of our credit facility limit the amount we can borrow to a borrowing base amount which is determined by our lenders in their sole discretion based on their valuation of our proved reserves and their internal criteria including commodity price outlook. The borrowing base amount is subject to redetermination semi-annually and for event-driven unscheduled redeterminations. Our next scheduled redetermination is OctoberApril 1, 2017.2018.

Under the credit facility, a cross default provision provides that any debt default of more than $75 million by Energen or Energen Resources will constitute an event of default by Energen.

The following is a summary of information relating to Energen’s credit facility:

The following is a summary of information relating to Energen’s interest expense:

*Included in Energen’s total interest expense. At JuneSeptember 30, 2017, Energen paid commitment fees on the unused portion of the available credit facility at a current annual rate of 30 basis points.

During the first quarter of 2016, Energen issued 18,170,000 additional shares of common stock through a public equity offering. We received net proceeds of approximately $381.1 million, after deducting offering expenses. Net proceeds from this offering were used to repay borrowings under our credit facility and for general corporate purposes.

Performance Share Awards: In addition, the Stock Incentive Plan provides for the grant of performance share awards to eligible employees based on predetermined Energen performance criteria at the end of an award period. The Stock Incentive Plan provides that payment of earned performance share awards be made in the form of Energen common stock. Performance share awards are valued using the Monte Carlo model which uses historical volatility and other assumptions to estimate the probability of satisfying the market condition of the award and have a three-year vesting period. A summary of performance share award activity during the sixnine months ended JuneSeptember 30, 2017 is presented below:

During the three months and sixnine months ended JuneSeptember 30, 2017, Energen had non-cash purchases of approximately $15,000$0.1 million and $3.2$3.3 million, respectively, of Energen common stock in conjunction with tax withholdings on other stock compensation and our non-qualified deferred compensation plan. Energen had non-cash purchases of Energen common stock of $19,000$0.1 million and $2.4$2.6 million during the three months and sixnine months JuneSeptember 30, 2016. Energen utilized internally generated cash flows in payment of the related tax withholdings.

In October 2014, Energen’s Board of Directors elected to freeze and terminate its qualified defined benefit pension plan. A plan amendment adopted in October 2014 closed the plan to new entrants, effective November 1, 2014, and froze benefit accruals effective December 31, 2014. Energen terminated the plan on January 31, 2015 and distributed benefits in December 2015. The Pension Benefit Guaranty Corporation (PBGC) is conducting an audit of the termination of the pension plan to ensure that Energen properly calculated and distributed benefits in accordance with plan provisions and in compliance with the appropriate laws and regulations administered by the PBGC.

Energen’s non-qualified supplemental retirement plans were terminated effective December 31, 2014. Distributions under the plans were partially made in the first quarter of 2015 with the remainder of approximately $14.5 million paid in the first quarter of 2016. The Company expects to make no additional benefit payments with respect to the termination of the non-qualified supplemental retirement plans. Certain annuities associated with our non-qualified supplemental retirement plans remain of approximately $1.0

million and $1.1 million and are included in other current liabilities and other long-term liabilities on the consolidated balance sheets at JuneSeptember 30, 2017 and December 31, 2016, respectively. In the first quarter of 2016, Energen incurred a settlement charge of $3.3 million for the payment of lump sums from the non-qualified supplemental retirement plans.

Energen provides certain postretirement health care and life insurance benefits for all employees hired prior to January 1, 2010. These postretirement healthcare and life insurance benefits are available upon reaching normal retirement age while working for Energen. The components of net periodic postretirement benefit income for Energen’s postretirement benefit plan were as follows:

There are no required contributions to the postretirement benefit plan during 2017. In the first quarter of 2016, Energen incurred a curtailment gain of $0.8 million in connection with the reduction in workforce.

On November 4, 2015, Energen Resources filed a quiet title action against Endeavor Energy Resources, L.P. (Endeavor) in the District Court of Howard County, Texas, to remove a cloud on the title to approximately 10,000 acres leased by Energen Resources in that county. Energen Resources believes the cloud on title arises from a prior, unreleased but partially terminated oil and gas lease covering the leased lands. The trial judge ruled with respect to the acreage not held by production that Endeavor’s lease terminated prior to the date Energen Resources entered into its lease. In November 2016, the trial judge entered a final judgment to that effect and that judgementjudgment has been appealed by Endeavor.

During January 2014, Energen Resources responded to a General Notice and Information Request from the Environmental Protection Agency regarding the Reef Environmental Site (the Site) in Sylacauga, Talladega County, Alabama. The letter identifies Energen Resources as a potentially responsible party under the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 for the cleanup of the Site. In 2008, Energen hired a third party to transport approximately 3,000 gallons of non-hazardous wastewater to Reef Environmental for wastewater treatment. Reef Environmental ceased operating its wastewater treatment system in 2010. Because it used Reef Environmental only one time for a small volume of non-hazardous wastewater, Energen Resources has not accrued a liability for cleanup of the Site.

Energen Resources appealed the Order in 2011 and in July 2012, on a motion from ONRR, the Order was remanded. In August 2014, ONRR issued its Revised Order and Energen Resources appealed the Revised Order. In the Revised Order, ONRR ordered that Energen pay additional royalties on production from certain federal leases in the amount of $129,700. At ONRR’s request, the Revised Order was also remanded in August 2015. On April 15, 2016, ONRR issued its Second Revised Order. The Second Revised Order directs Energen Resources to pay additional royalties of $189,000, replacing the previous demand of $129,700. Energen estimates that application of the ONRR position to all of the Company’s federal leases would result in ONRR claims up to approximately $24 million, plus interest and penalties from 2004 forward. ONRR began implementing its unbundling initiative in 2010, but seeks to implement its revisions retroactively, despite the fact that they conflict with previous audits, allowances and industry practice. Energen is contesting the Second Revised Order, the predecessor orders and the findings. Management is unable, at this time, to determine a range of reasonably possible losses, and no amount has been accrued as of JuneSeptember 30, 2017.

Energen capitalizes exploratory drilling costs until a determination is made that the well or project has either found proved reserves or is impaired. After an exploratory well has been drilled and found oil and natural gas reserves, a determination may be pending as to whether the oil and natural gas quantities can be classified as proved. In those circumstances, Energen continues to capitalize the drilling costs pending the determination of proved status if (i) the well has found a sufficient quantity of reserves to justify its completion as a producing well and (ii) Energen is making sufficient progress assessing the reserves and the economic and operating viability of the project. Capitalized exploratory drilling costs are presented in proved properties in the balance sheets. If the exploratory well is determined to be a dry hole, the costs are charged to exploration expense. Other exploration costs, including geological and geophysical costs, are expensed as incurred.

The following table sets forth capitalized exploratory well costs and includes additions pending determination of proved reserves, reclassifications to proved reserves and costs charged to expense:

The following table sets forth capitalized exploratory well costs:

At JuneSeptember 30, 2017, Energen had 5155 gross exploratory wells either drilling or waiting on results from completion and testing, all of which were located in the Permian Basin. As of JuneSeptember 30, 2017, the Company had no wells capitalized greater than a year. As of December 31, 2016, the Company had two gross wells capitalized greater than a year, which were completed during 2017.

Energen’s asset retirement obligations (ARO) primarily relate to the future plugging, abandonment and reclamation of wells and facilities. We recognize a liability for the fair value of the ARO in the periods incurred. The ARO fair value liability is determined by calculating the present value of the estimated future cash outflows, adjusted for inflation, we expect to incur to plug, abandon and reclaim our producing properties at the end of their productive lives, and is recognized on a discounted basis incorporating an estimate of performance risk specific to Energen. Subsequent to initial measurement, liabilities are accreted to their present value and capitalized costs are depreciated over the estimated useful lives of the related assets. Upon settlement of the liability, Energen may recognize a gain or loss for differences between estimated and actual settlement costs.

The following table reflects the components of the change in Energen’s ARO balance:

The following table provides changes in the components of accumulated other comprehensive income (loss), net of the related income tax effects.

Non-cash impairment writedowns are reflected in asset impairment on the consolidated statements of operations.

In the year-to-date 2017, Energen recognized unproved leasehold writedowns primarily on Permian Basin oil properties of $0.4$0.5 million. Energen recognized unproved leasehold writedowns primarily on Permian Basin oil properties in the Delaware Basin and the Central Basin Platform of $4.1$4.7 million in the first quarter ofyear-to-date 2016.

During the sixnine months ended JuneSeptember 30, 2017, Energen completed an estimated total of $235.6$259.3 million in various purchases and renewals of unproved acquisitions, which are accounted for as asset acquisitions, including approximately $185.9$208.1 million in the Delaware Basin and approximately $30.9$32.4 million in the Midland Basin for unproved leasehold and $18.8 million for mineral purchases in the Delaware Basin. During the sixnine months ended JuneSeptember 30, 2016, Energen completed an estimated $27.2$134.9 million in various purchases and renewals of unproved leasehold largely in the Permian Basin.Basin, including approximately $77 million of acreage purchased in Lea County, New Mexico.

During June, July and August of 2016, Energen completed a series of asset sales of certain non-core Permian Basin assets in the Delaware Basin in Texas and in the San Juan Basin in New Mexico for an aggregate purchase price of $552 million. These transactions had closing dates of June 3, June 7, June 30, July 15 and August 9 of 2016 with various effective dates ranging from March 1, 2016 to June 30, 2016. Minor portions of the assets were transferred to other parties upon the exercise of preferential purchase rights under pre-existing joint operating agreements in the ordinary course of business. Pre-tax proceeds to Energen were approximately $532.5$532.4 million after purchase price adjustments of approximately $19 million related to the operations of the properties subsequent to the effective dates and other one-time adjustments including transfer payments and certain amounts due to the buyer, but before consideration of transaction costs of approximately $5 million. Energen recognized total net pre-tax gains of approximately $246 million on the sales. Energen used proceeds from the sale to fund ongoing operations. For the sixnine months ended JuneSeptember 30, 2017, included in the net (gain) lossgain on sale of assets and other, Energen recognized post-closing adjustment losses of $0.2$0.4 million on these sales. For the sixthree and nine months ended JuneSeptember 30, 2016, Energen recognized pre-tax gains of $161.1$91.4 million and $252.4 million, respectively, on the sales closed through June 30, 2016.sales. Energen used proceeds from the sale to fund ongoing operations.

In May 2017, the Financial Accounting Standards Board (FASB) issued Accounting Standard Update (ASU) No. 2017-09, Stock Compensation - Scope of Modification Accounting. The amendments in this update provide guidance about which changes to the

terms or conditions of a share-based payment award require an entity to apply modification accounting. The amendment is effective for annual periods beginning after December 15, 2017, and interim periods within those annual years. This amendment is not expected to have a material impact to the Company’s financial position or results of operations.

In March 2017, the FASB issued ASU No. 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. The amendments in this update require that the service cost component of net periodic postretirement benefit expense be presented in the same statement of operations line item as other employee compensation costs, while the remaining components of net periodic postretirement benefit expense are to be presented outside operating income. The amendment is effective for annual periods beginning after December 15, 2017, and interim periods within those annual years. This amendment is not expected to have a material impact to the Company’s financial position or results of operations.

In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows - Classification of Certain Cash Receipts and Cash Payments. This update apples to all entities that are required to present a statement of cash flows. This update provides guidance on eight specific cash flow issues: debt prepayment or debt extinguishment costs, settlement of zero-coupon debt instruments or other debt instruments with coupon interest rates that are insignificant in relation to the effective interest rate of the borrowing, contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate-owned life insurance policies, distributions received from equity method investees, beneficial interests in securitization transactions and separately identifiable cash flows and application of the predominance principle. This update will be effective for financial statements issued for fiscal years beginning after December 31, 2017, including interim periods within those fiscal years with early adoption permitted. This update will be applied using the retrospective transition method. Adoption of this standard will only affect the presentation of the Company’s cash flows and is not expected to have a material impact on the Company’s consolidated financial statements.

In March 2016, the FASB issued ASU No. 2016-09, Improvements to Employee Share-Based Payment Accounting, which makes a number of changes meant to simplify and improve accounting for share-based payments. The amendment was effective for annual periods beginning after December 15, 2016, and interim periods within those annual periods. The adoption of this ASU effective January 1, 2017 did not have a material impact on our consolidated financial statements. Upon adoption of this new guidance, all excess tax benefits and tax deficiencies are recognized as income tax expense or benefit in our consolidated statements of operations as a discrete item in the reporting period in which they occur. The presentation requirements for cash flows related to employee taxes paid for withheld shares were adjusted retrospectively. These cash outflows, which were historically presented as an operating activity, were classified as a financing activity under taxes paid for shares withheld on the consolidated statements of cash flows. The Company also had an approximate $169,000 decrease to retained earnings associated with our election to recognize forfeitures as they occur.

In February 2016, the FASB issued ASU No. 2016-02, Leases. This update increases transparency and comparability by recognizing lease assets and lease liabilities on the balance sheet and disclosing key information about leasing arrangements. The amendment is

In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers. This update is based on the principle that revenue is recognized to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. It also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts. Companies may apply this update retrospectively or using a modified retrospective approach to adjust retained earnings. In August 2015, the FASB issued ASU No. 2015-14, Revenue from Contracts with Customers, which deferred the effective date of ASU No. 2014-09 to annual periods beginning after December 15, 2017, including interim reporting periods within that reporting period. The Company expects to adopt this standard using the modified retrospective method of adoption on January 1, 2018. We continue to evaluate the impact of this standard on our individual customer contracts; however, due to the short length of our revenue cycle, we do not expect and have not identified any significant impacts to our consolidated financial statements.

Energen Corporation (Energen or the Company) is an oil and natural gas exploration and production company engaged in the exploration, development and production of oil, natural gas liquids and natural gas. Our operations are conducted through our subsidiary, Energen Resources Corporation (Energen Resources) and primarily occur within the Midland Basin, the Delaware Basin and the Central Basin Platform areas of the Permian Basin in west Texas and New Mexico.

Energen is focused on increasing its oil, natural gas liquids and natural gas production and proved reserves largely through active development and/or exploratory programs in the Permian Basin. The Company seeks to expand its footprint primarily through acquisitions of proved properties and unproved leasehold within areas of existing operations. All oil, natural gas liquids and natural gas production is sold to third parties. Energen operates properties for its own interest and that of its joint interest owners. This role includes overall project management and day-to-day decision-making relative to project operations.

Energen had a net incomeloss of $29.5$18.5 million ($0.300.19 per diluted share) for the three months ended JuneSeptember 30, 2017 as compared with net income of $36.8$53.3 million ($0.380.55 per diluted share) for the same period in the prior year. This change in net income was primarily the result of:

Energen had net income of $62.9$44.4 million ($0.640.45 per diluted share) for the sixnine months ended JuneSeptember 30, 2017 as compared with net loss of $166.4$113.0 million ($1.811.21 per diluted share) for the same period in the prior year. This increasechange in net income was primarily the result of:

Capital expenditures in the Permian Basin by area during 2017 are planned as follows:

To finance our capital spending, we expect to use cash flow from operations supplemented by our existing syndicated credit facility. Capital spending is required to offset declines in production and proved oil and natural gas reserves. Future success in maintaining and growing reserves and production is highly dependent on the results of our drilling program and our ability to add reserves economically during a challengingvolatile market for crude oil and natural gas.

Energen also may allocate additional capital for other oil and natural gas activities such as property acquisitions and additional development of existing properties. Energen may evaluate acquisition opportunities which arise in the marketplace. Energen’s ability to invest in property acquisitions is subject to market conditions and industry trends. Property acquisitions, except as disclosed above, are not included in the aforementioned estimate of oil and natural gas investments and could result in capital expenditures different from those outlined above.

The following table summarizes information regarding our production and operating data.