UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of

the Securities Exchange Act of 1934

Date of Report February 17, 2016

(205) 326-2700

(Registrant’s telephone number including area code)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Section 1 – Registrant’s Business and Operations

Item 1.01 Entry into a Material Definitive Agreement

On February 17, 2016, Energen Corporation (“Energen”) entered into an Underwriting Agreement (the “Underwriting Agreement”) with Credit Suisse Securities (USA) LLC (the “Underwriter”). The Underwriting Agreement relates to a public offering and sale by Energen (the “Firm Share Offering”) of 15,800,000 shares of its common stock, par value $0.01 per share (the “Common Stock”), at a price to the Underwriter of $20.99 per share (the “Purchase Price”). Pursuant to the Underwriting Agreement, Energen granted the Underwriter a 30-day option to purchase up to an additional 2,370,000 shares of Common Stock on the same terms (the “Optional Share Offering” and, together with the Firm Share Offering, the “Offering”), which option was exercised in full on February 17, 2016.

The Offering closed on February 22, 2016. Energen received net proceeds of approximately $381.1 million (after deducting estimated offering expenses) from the Offering. Energen intends to use the net proceeds from the Offering to repay borrowings under its credit facility, to fund drilling and development activities, and/or for other general corporate purposes.

The Underwriting Agreement contains customary representations, warranties and agreements by Energen and customary conditions to closing, obligations of the parties and termination provisions. Energen has agreed to indemnify the Underwriter against certain liabilities, including liabilities under the Securities Act of 1933, as amended (the “Securities Act”), and the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or to contribute to payments the Underwriter may be required to make because of any of those liabilities.

The Offering was made pursuant to Energen’s effective automatic shelf registration statement on Form S-3 (File No. 333-203914), filed with the Securities and Exchange Commission (the “Commission”) on May 6, 2015 (the “Registration Statement”), and a prospectus, which consists of a base prospectus, filed with the Commission on May 6, 2015, a preliminary prospectus supplement, filed with the Commission on February 17, 2016, and a final prospectus supplement, filed with the Commission on February 19, 2016 (collectively, the “Prospectus”).

In the ordinary course of its business, the Underwriter (directly or through affiliates) has engaged, and may in the future engage, in commercial banking, investment banking, financial advisory or other services to Energen and its affiliates for which it has in the past and may in the future receive customary compensation and expense reimbursement.

The preceding summary of the material terms of the Underwriting Agreement is qualified in its entirety by the full text of such agreement, which is filed herewith as Exhibit 1.1. In the event of any discrepancy between the preceding summary and the text of the Underwriting Agreement, the text of the Underwriting Agreement shall control.

Section 7 – Regulation FD

Item 7.01 Regulation FD Disclosure.

On February 17, 2016, Energen announced that it had commenced the Offering described in Item 1.01 of this Current Report on Form 8-K. A copy of the press release is furnished as Exhibit 99.1 to this Current Report on Form 8-K.

On February 17, 2016, Energen announced that it had priced the Offering described in Item 1.01 of this Current Report on Form 8-K. A copy of the press release is furnished as Exhibit 99.2 to this Current Report on Form 8-K.

On February 22, 2016, Energen announced that (a) the Underwriter had exercised its option to purchase the additional 2,370,000 shares of Common Stock pursuant to the Optional Share Offering and (b) Energen had closed the Offering and received net proceeds of $381.1 million (after deducting estimated offering expenses), in each case as described in Item 1.01 of this Current Report on Form 8-K. A copy of the press release is furnished as Exhibit 99.3 to this Current Report on Form 8-K.

The information furnished in this Item 7.01 shall not be deemed to be “filed” for purposes of Section 18 of the Exchange Act, or otherwise subject to the liabilities of that section, nor shall such information be deemed to be incorporated by reference into any of Energen’s filings under the Securities Act or the Exchange Act.

Section 9 Financial Statements and Exhibits

Item 9.01 Financial Statements and Exhibits

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

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