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

August 8, 2012

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:

Item 1.01. Entry into a Material Definitive Agreement.

On August 8, 2012, Atmos Energy Corporation (“Atmos Energy”) entered into a definitive agreement (the “Agreement”) to sell its natural gas distribution operations in Georgia (the “Business”) to Liberty Energy (Georgia) Corp. (“Liberty Energy”), an affiliate of Algonquin Power & Utilities Corp. (“Algonquin”), for a purchase price of approximately $141 million. The Agreement contains the usual terms and conditions customary for transactions of this type, including adjustments to the purchase price at closing, if applicable, and indemnification by Atmos Energy related to representations and warranties regarding the Business. The closing of the transaction is subject to the satisfaction of customary conditions, including the receipt of applicable regulatory approvals. Neither Atmos Energy nor any of its affiliates have had a material relationship with either Liberty Energy or Algonquin, other than in respect of the Agreement and the sale by Atmos Energy to Liberty Energy (Midstates) Corp. of its natural gas distribution operations in Missouri, Illinois and Iowa, which sale closed on August 1, 2012.

In addition, on August 8, 2012, in connection with the execution of the Agreement, Algonquin executed a guaranty (the “Guaranty”) of the obligations of Liberty Energy under the Agreement. A copy of the Agreement and the Guaranty are filed as Exhibits 2.1 and 10.1, respectively and are incorporated herein by reference. The foregoing summary does not purport to be complete and is qualified in its entirety by reference to the Agreement and the Guaranty.

The Agreement contains representations, warranties and disclosures that were made by the parties to each other as of specific dates and to evidence their agreement on various issues. The assertions and other statements or disclosures embodied in these representations, warranties and disclosures were made solely for purposes of the Agreement and may be subject to important qualifications and limitations or other factors agreed to by the parties in connection with negotiating the terms of the transaction. Moreover, certain of these representations, warranties and disclosures may not be accurate and complete as of any specified date because they may be subject to contractual standards of materiality that differ from standards generally applicable to investors and have been used to allocate risk among the parties rather than to establish matters as facts or otherwise. Based on the foregoing, you should not rely on the representations, warranties and disclosures included in the Agreement as statements of factual information.

Item 2.02. Results of Operations and Financial Condition.

On Wednesday, August 8, 2012, Atmos Energy issued a news release in which it reported the Company’s financial results for the third quarter of the 2012 fiscal year, which will end September 30, 2012, and that certain of its officers would discuss such financial results in a conference call on Thursday, August 9, 2012 at 10:00 a.m. Eastern Time. In the release, the Company also announced that the call would be webcast live and that slides for the webcast would be available on its website for all interested parties.

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A copy of the news release is furnished as Exhibit 99.1. The information furnished in this Item 2.02 and in Exhibit 99.1 shall not be deemed to be “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 or otherwise subject to the liabilities of that section, nor shall such information be deemed to be incorporated by reference into any of Atmos Energy’s filings under the Securities Act of 1933 or the Securities Exchange Act of 1934.

On August 8, 2012, Atmos Energy announced in a news release that it had entered into the Agreement described above under Item 1.01. A copy of the news release is furnished as Exhibit 99.2. The information furnished in this Item 7.01 and in Exhibit 99.2 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 Atmos Energy’s filings under the Securities Act of 1933 or the Securities Exchange Act of 1934.

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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.

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INDEX TO EXHIBITS

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