UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 6)*

ENERGEN CORPORATION

(Name of Issuer)

COMMON STOCK, $0.01 PAR VALUE

(Title of Class of Securities)

29265N108

(CUSIP Number)

Keith Meister

Patrick J. Dooley, Esq.

Corvex Management LP

667 Madison Avenue

New York, NY 10065

(212) 474-6700

Jeffrey L. Kochian

Akin Gump Strauss Hauer & Feld LLP

One Bryant Park

New York, NY 10036

(212) 872-8069

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

September 14, 2017

(Date of Event Which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.  ☐

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See §240.13d-7 for other parties to whom copies are to be sent.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

This Amendment No. 6 supplements the information set forth in the Schedule 13D filed by Corvex Management LP and Keith Meister with the United States Securities and Exchange Commission (the “SEC”) on May 31, 2017, as previously amended (the “Schedule 13D”), relating to the shares of common stock, par value $0.01 per share (the “Shares”), of Energen Corporation, an Alabama corporation (the “Issuer”). Capitalized terms used but not defined herein shall have the meanings ascribed to them in the Schedule 13D.

The information set forth in response to each separate Item below shall be deemed to be a response to all Items where such information is relevant. The Schedule 13D is supplementally amended as follows.

Item 4. Purpose of Transaction

As previously stated in the Schedule 13D, as holders of 10% or more of the outstanding Shares, the Reporting Persons believe that Alabama law permits the Corvex Funds to cause the Issuer to call a special meeting of shareholders at which shareholders will be able to vote on matters proposed by the Reporting Persons, including proposals to increase the size of the Board to up to 15 directors, and to fill the vacancies created by such expansion with nominees proposed by the Reporting Persons.

On September 12, 2017, the Issuer filed a Complaint for Declaratory Judgment and Injunctive Relief and related documents in state court in Alabama seeking, among other things, an order that the Board of the Issuer has the sole right to determine the number of directors and that any vacancy resulting from an increase in the size of the Board can be filled by, and only by, the existing Board - in each case, to the exclusion of shareholders. The Reporting Persons believe they have the right to take the actions described above and will aggressively seek to enforce their right to take such actions.

In light of the filing of the litigation, the Reporting Persons sent a letter to the Board of the Issuer on September 14, 2017, which is attached hereto as Exhibit 9 and is incorporated herein by reference.

The Reporting Persons intend to review their investment in the Issuer on a continuing basis and may from time to time and at any time in the future depending on various factors, including, without limitation, the Issuer’s financial position and strategic direction, actions taken by the Board, price levels of the Shares, other investment opportunities available to the Reporting Persons, conditions in the securities market and general economic and industry conditions, take such actions with respect to their investments in the Issuer as they deem appropriate, which may include further discussions with the Issuer regarding matters previously disclosed in this Schedule 13D, as amended, as well as seeking direct discussions with, and changes or additions to, the Board. These actions may include, without limitation: (i) acquiring additional Shares and/or other equity, debt, notes, other securities, or derivative or other instruments that are convertible into Shares, or are based upon or relate to the value of the Shares or the Issuer (collectively, “Securities”) in the open market or otherwise; (ii) disposing of any or all of their Securities in the open market or otherwise; (iii) engaging in any hedging or similar transactions with respect to the Securities; or (iv) proposing or considering one or more of the actions described in subsections (a) through (j) of Item 4 of Schedule 13D.

Item 7. Material to be Filed as Exhibits

Exhibit 9 – Letter to the Board of Directors of Energen Corporation, dated September 14, 2017

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Exhibit 9

September 14, 2017

Board of Directors

Energen Corporation

605 Richard Arrington Jr. Blvd. N.

Birmingham, AL 35203

Ladies and Gentlemen:

As you are aware, Corvex has engaged in an open and constructive dialogue with your Chief Executive Officer and Chairman, James McManus, for several months. Stated in your own words, Corvex and Energen’s Board of Directors share a common goal: to maximize value for all shareholders. Therefore, you can understand our extreme disappointment on September 12^th when Mr. McManus told us that the Board had rejected our proposal to add three highly-qualified, independent individuals to the Energen board, without the nominating and governance committee ever speaking with the candidates. Even more stupefying is Energen’s decision to preemptively sue us—the Company’s largest shareholder—simply to prevent your shareholders from gathering at a special meeting in order to have their voices heard. Your actions speak volumes; instead of welcoming shareholder engagement, you are attempting to hide behind the Court.

Indeed, we believe the primary goal of this litigation is to unduly preclude—or at least delay—your shareholders’ ultimate right to vote in a manner that is consistent with their interests as owners of your Company. You may position the lawsuit as a clarification of corporate provisions, but make no mistake about it: the clear effect is an effort to disenfranchise shareholders by denying them the right to decide the composition of Energen’s board. Rather than using our discussions as an opportunity to demonstrate a strong commitment to open and sound corporate governance practices, you are actively taking a step in the other direction. Nevertheless, we firmly believe that Alabama law and the Company’s Charter permit shareholders to vote on our proposal to expand the board, and permits Corvex, as a 10%-plus shareholder, to compel the scheduling of a special meeting to vote on such proposal. We will aggressively defend our right to call that meeting, and we will not rest until shareholders’ voices are heard.

As a reminder, we have stated clearly that we believe the Company has highly valuable assets in the Permian Basin. Despite this enviable position, we believe Energen trades at a discount to its public peers—an assertion with which Mr. McManus has agreed. Further, and more importantly, Energen currently trades at a material discount to its net asset value (NAV), another point with which Mr. McManus has emphatically agreed. We believe this discount is due, in part, to the Company’s track record of operating performance and capital allocation, both of which fall short of its best-in-class peers. In addition, we believe that the Company’s suboptimal corporate governance structure has magnified the prevailing discount to NAV. Among other examples, Energen’s corporate governance failings are evidenced by: 1) the board’s unwillingness to allow its lead director (or any other director) to meet shareholders directly, without senior management’s chaperoned influence; and 2) the board’s highly abbreviated and disingenuous strategic review process. Finally, we have stated that the case for M&A is simply too compelling to ignore, given the Company’s asset position and the significant benefits that could be unlocked through consolidation.

In June, 2017, we asked the Company to do two things: 1) announce that it has hired a bank to seriously explore strategic alternatives, and 2) meet with top shareholders to get their views on the value of various alternatives that could be available to the Company. We were clear that we had not pre-judged any outcome, and would support whichever decision created the most value for all shareholders. However, you took neither of our suggested actions. Instead, a mere three weeks after

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our June letter, you announced that you had reviewed strategic alternatives and were recommitting to the Company’s status quo business plan. The board refused to meet with us and did not engage in any formal process to solicit the views of other shareholders. We urged you to meet with shareholders and reconsider your conclusion—a suggestion which you also rejected.

We then engaged in discussions with you about adding a number of new, highly qualified directors to contribute fresh perspectives to the boardroom. If you had taken the time to meet our proposed candidates, we believe that you would be hard-pressed to dispute their extraordinary industry knowledge coupled with extensive C-suite and public-company boardroom experience. However, instead of constructively engaging with us and meeting these director candidates, you filed a lawsuit asking a court to bless your interpretation of Alabama law that would strip shareholders of their right to expand the board. It is for this reason we feel compelled to write the letter you are reading now.

Let me be clear, you will face shareholders one way or the other. This litigation will cost shareholders valuable resources, act as a distraction to management, and will ultimately only serve to delay the inevitable. Shareholders will eventually get their vote, either at a special meeting we would like to call or at Energen’s next annual meeting. Moreover, what you would view as a “win” in court will be widely considered a loss for the shareholders you represent. If you prevail in this lawsuit—which we intend to vigorously contest—you only will have further highlighted Energen’s suboptimal approach to corporate governance. Indeed, this lawsuit represents yet another example in what is becoming a disconcerting pattern of events that calls into question how this board and management apply their judgment and energy.

As always, despite our differences, I continue to hope that we are aligned in our goal to create the most risk-adjusted value for shareholders. In that regard, I remain willing and ready to discuss these issues with any member of the board, and to work constructively, as team-members, with no preconceived outcomes other than a goal to maximize value for all shareholders.

Sincerely,

/s/ Keith Meister

Keith Meister

Managing Partner

Corvex Management

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