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

February 11, 2014

Date of Report (Date of earliest event reported)

ATMOS ENERGY CORPORATION

(Exact Name of Registrant as Specified in its Charter)

(972) 934-9227

(Registrant’s Telephone Number, Including Area Code)

Not Applicable

(Former Name or Former Address, if Changed Since Last Report)

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:

On February 11, 2014, Atmos Energy Corporation (“Atmos Energy”) entered into an underwriting agreement (the “Underwriting Agreement”) with J.P. Morgan Securities LLC and Goldman, Sachs & Co. as representatives of the several underwriters named in Schedule I thereto (the “Underwriters”), with respect to the offering and sale in an underwritten public offering (the “Offering”) by the Underwriters of 9,200,000 shares of Atmos Energy’s common stock, no par value, including 1,200,000 shares pursuant to the exercise by the Underwriters of their option to purchase additional shares. The Underwriting Agreement is filed herewith as Exhibit 1.1.

The Offering has been registered under the Securities Act pursuant to a registration statement on Form S-3 (Registration No. 333-187606) of Atmos Energy (the “Registration Statement”), and a prospectus supplement dated February 11, 2014, which was filed with the Securities and Exchange Commission pursuant to Rule 424(b) of the Securities Act on February 12, 2014. Legal opinions related to the Registration Statement are also filed herewith as Exhibits 5.1 and 5.2. At the closing of the Offering on February 18, 2014, Atmos Energy will receive net proceeds, after the underwriting discount but before other offering expenses, of approximately $391 million.

SIGNATURE

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 hereunto duly authorized.

INDEX TO EXHIBITS