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 (Date of earliest event reported): July 10, 2015

DUNE ENERGY, INC.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (713) 229-6300

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 (see General Instruction A.2 below):

Item 1.01. Entry into a Material Definitive Agreement.

As previously disclosed in Current Report on Form 8-K (the “Prior Form 8-K”) filed by Dune Energy, Inc. (the “Company”) on March 12, 2015, the Company and its subsidiaries (collectively with the Company, the “Debtors”) filed voluntary petitions in the United States Bankruptcy Court for the Western District of Texas, Austin Division (the “Bankruptcy Court”) on March 8, 2015 seeking relief under Chapter 11 of Title 11 of the United States Code (the “Bankruptcy Code”). The Chapter 11 cases are being jointly administered under the caption “In re Dune Energy, Inc., et al”, Case No. 15-10336 (the “Chapter 11 Cases”).

Since the filing of the Prior Form 8-K, on April 8, 2015, a bidding procedures order was entered by the Bankruptcy Court establishing procedures for the sale of substantially all of the assets of the Debtors, pursuant to which, among other things, qualified bidders would submit qualifying bids by June 5, 2015 (the “Bidding Procedures Order”). Following entry of the Bidding Procedures Order, the Debtors determined to extend the bid deadline until June 19, 2015. On June 30, 2015, the Debtors conducted the Auction contemplated by the Bidding Procedures Order (the “Auction”). At the conclusion of the Auction, Trimont Energy (NOW), LLC (“Trimont”) and White Marlin Oil and Gas Company, LLC (“White Marlin”) were declared the successful bidders with respect to two different asset packages in accordance with the Bidding Procedures Order for the Auction. Trimont was declared the backup successful bidder in the event the sale to White Marlin fails to close.

Trimont’s bid included that certain Purchase and Sale Agreement dated as of June 30, 2015, as amended (the “Trimont PSA”). White Marlin’s bid included that certain Purchase and Sale Agreement dated as of June 24, 2015, as amended (the “White Marlin PSA”). Pursuant to the Trimont PSA, Trimont agreed to purchase the Garden Island Bay field and the Bateman Lake field from the Debtors for $1, the assumption of real estate tax liabilities and the assumption of all related plugging and abandonment liabilities. Trimont also agreed to assume certain of the Debtors’ executory contracts and pay costs necessary to cure defaults under such contracts. Pursuant to the White Marlin PSA, White Marlin agreed to purchase Abbeville North, Bayou Couba, Chocolate Bayou, Comite, Lake Bouef SW, Leeville, Los Mogotes, Malo Domingo, Manchester SW, Manchester W, and Toro Grande Fields from the Debtors for $19 million and the assumption of plugging and abandonment liabilities as set forth in the White Marlin PSA. White Marlin also agreed to assume certain of the Debtors’ executory contracts and pay costs necessary to cure defaults under such contracts. The Trimont PSA and the White Marlin PSA contain customary representations and warranties as well as various covenants. The closing of the transactions contemplated by the Trimont PSA and the White Marlin PSA are subject to various conditions precedent as specified in each agreement, including the entry of orders of the Bankruptcy Court approving each agreement. On July 10, 2015, the Bankruptcy Court entered orders approving the sales on the terms set forth in the Trimont PSA and the White Marlin PSA. The Bankruptcy Court Sale Orders are filed as Exhibits 99.1 and 99.2 hereto and incorporated herein by reference. Following the Bankruptcy Court’s approval of the Trimont PSA and the White Marlin PSA, on July 15, 2015, the Debtors entered into the Trimont PSA and the White Marlin PSA.

The foregoing descriptions of the Trimont PSA and the White Marlin PSA do not purport to be complete and are qualified in their entirety by reference to the Trimont PSA and the White Marlin PSA filed as Exhibits 10.1 and 10.2, respectively, hereto and incorporated herein by reference.

Item 7.01. Regulation FD Disclosure.

Based on the Company’s debt and other obligations, the Company does not expect to be able to distribute any proceeds as a result of the Chapter 11 Cases to the Company’s stockholders and therefore believes that the shares of its common stock are worthless.

Additional information on the Chapter 11 Cases, including access to documents filed with the Bankruptcy Court and other general information about the Chapter 11 Cases, is available at https://cases.primeclerk.com/duneenergy/.

The information included in this Item 7.01 to this Current Report on Form 8-K shall not be deemed “filed” for purposes of or otherwise subject to the liabilities under Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). Unless expressly incorporated into a filing of the Company under the Securities Act of 1933, as amended, or the Exchange Act made after the date hereof, the information contained in this Item 7.01 shall not be incorporated by reference into any of our filings, whether made before or after the date hereof, regardless of any general incorporation language in any such filing.

Cautionary Statement Regarding Forward-Looking Statements

This Current Report on Form 8-K contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Forward-looking statements are those involving future events and future results that are based on current expectations, estimates, forecasts, and projections, as well as the current beliefs and assumptions of the Company’s management. When used in this document, the words such as “anticipate”, “estimate”, “expect”, “project”, “intend”, “plan”, “believe”, “may”, “predict”, “will”, “would”, “could”, “should”, “target” and similar expressions are forward-looking statements. All statements contained in this Current Report that are not statements of historical fact and other estimates, projections, future trends and the outcome of events that have not yet occurred referenced in this Form 8-K should be considered forward-looking statements. Although the Company believes that its expectations reflected in these forward-looking statements are reasonable, such statements involve risks and uncertainties and no assurance can be given that actual results will be consistent with these forward-looking statements. Important factors that could cause actual results to differ from these forward-looking statements include extension of the debtor-in-possession financing until a closing of a sale of assets occurs pursuant to Section 363 of the Bankruptcy Code; the Company’s ability to obtain Bankruptcy Court approval with respect to motions in the Chapter 11 Cases; the ability of the Company and its subsidiaries to prosecute, develop and consummate one or more plan of liquidation with respect to the Chapter 11 Cases; Bankruptcy Court rulings in the Chapter 11 Cases and the outcome of the cases in general; the length of time the Company will operate under the Chapter 11 Cases; risks associated with third party motions in the Chapter 11 Cases; the potential adverse effects of the Chapter 11 proceedings on the Company’s liquidity, results of operations or business prospects; increased legal costs related to the Chapter 11 Cases and other litigation; the Company’s ability to generate or raise cash and maintain a cash balance sufficient to maintain its assets during the pendency of the Chapter 11 Cases; the effects of the bankruptcy filing on the Company and its subsidiaries and the interests of various creditors, equity holders and other constituents; the potential that the Company’s projects will experience technological and mechanical problems, geological conditions may not result in commercial levels of oil and gas production; changes in product prices and other risks disclosed in the Company’s Annual Report on Form 10-K for the year ended December 31, 2013 and quarterly and current reports on Form 10-Q and 8-K filed with the U.S. Securities and Exchange Commission. There may be other factors that may cause the Company’s actual results to differ materially from the forward-looking statements. The Company undertakes no obligation to update or revise forward-looking statements to reflect events or circumstances that arise after the date made or to reflect the occurrence of unanticipated events.

Item 9.01. Financial Statements and Exhibits.

(d) 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 hereunto duly authorized.