13D Filing: Corvex Capital and Energen Corporation (EGN)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 8)*

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)

January 2, 2018

(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. 8 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.

The Reporting Persons used the working capital of the
Corvex Funds to purchase the 8,254,426 Shares reported herein and to acquire the call options referenced in Item 5. The total purchase price for the Shares reported herein was approximately $430,853,232.65 and the purchase price to acquire such call
options was approximately $25,582,763.70.

Various of the Reporting Persons may effect purchases of securities through margin accounts maintained for the
Corvex Funds with brokers, which extend margin credit as and when required to open or carry positions in their margin accounts, subject to applicable federal margin regulations, stock exchange rules and such firms credit policies. Positions in
Shares may be held in margin accounts and may be pledged as collateral security for the repayment of debit balances in such accounts.

In connection with portfolio management activities as between certain of the
Corvex Funds, Corvex sold 40,000 Shares in open market transactions on December 28, 2017, at a weighted average price of $57.4626 per Share and sold 40,294 Shares in open market transactions on December 29, 2017, at a weighted average
price of $57.6619 per Share and on January 2, 2018 sold an aggregate of 1,456,048 Shares at $57.57 per Share in privately negotiated transactions and in connection therewith on January 2, 2018 acquired the call options referencing
1,456,048 Shares and sold the put options referencing 1,456,048 Shares as described in Item 5.

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 Issuers 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 well as seeking direct discussions with, and changes or additions to, the Board, including by virtue of increasing
their share ownership back to a level that would permit the calling of a special meeting to expand the Board and filling newly created vacancies, or alternatively, at any level of share ownership, seeking to propose such action at an annual meeting
of shareholders, in either case if it is ultimately determined by the Supreme Court of Alabama that a shareholder is permitted to take such action. 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.

(a)-(b) Corvex may be deemed to be the beneficial owner of
8,254,426 Shares and 1,456,048 Shares underlying the call options referenced below in this Item 5, which collectively represent approximately 9.9% of the Issuers outstanding Shares. By virtue of his position as control person of the general
partner of Corvex, Mr. Meister may be considered to beneficially own such Shares. The Reporting Persons may be deemed to have sole power to vote and sole power to dispose of 9,710,474 Shares.

The percentage calculated in the immediately foregoing paragraph is calculated based on a total of 97,201,944
Shares outstanding as of October 31, 2017, as reported in the Issuers Quarterly Report on Form 10-Q filed with the SEC on November 8, 2017.

The call options referenced above and in Item 4 are over-the-counter market
American-style call options referencing an aggregate of 1,456,048 Shares, which have an exercise price of $40 per Share and expire on January 31, 2019. Such options were acquired for a premium of $17.58 per option.

In addition, as referenced in Item 4, Corvex sold over-the-counter market
European-style put options referencing an aggregate of 1,456,048 Shares, which have an exercise price of $40 per Share and expire on January 31, 2019 or the date on which the corresponding American-style call option described above in this Item
5 is exercised. Such options were sold for a premium of $0.01 per option.

Also, as previously disclosed, Corvex has sold listed American-style put
options referencing an aggregate of 415,200 Shares with an exercise price of $40 per Share, which expire on January 19, 2018.

(c) Except as set
forth in this Schedule 13D, there have been no transactions in the Shares during the sixty days prior to the date hereof by any of the Reporting Persons.

(d) The limited partners of (or investors in) each of the private investment funds for which Corvex or its affiliates acts as general partner and/or
investment adviser have the right to participate in the receipt of dividends from, or proceeds from the sale of, the Shares held for the accounts of their respective funds in accordance with their respective limited partnership interests (or
investment percentages) in their respective funds.

(e) Not applicable.

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.