Exhibit 99.1

For immediate release

Endeavour Announces Fourth Quarter and Year-End 2011

Financial and Operational Results

Houston, February 29, 2012 – Endeavour International Corporation (NYSE: END) (LSE: ENDV) today reported fourth quarter 2011 net income (loss), as adjusted of $(5.8) million compared to $81.1 million for 2010, when it reported an $87 million gain on the sale of its North Sea asset Cygnus. On a GAAP basis, net loss for the fourth quarter of 2011 was $44.6 million as compared to net income of $82.8 million for the same quarter in 2010. Production for the fourth quarter 2011 averaged approximately 4,100 barrels of oil equivalent per day (“boepd”).

Fourth quarter business highlights include:

“2011 was a pivotal year for Endeavour as we positioned the company for the next stage of its evolution. Although the anticipated production from Bacchus was delayed, the Company successfully reached key milestones to move the Rochelle project closer to its start-up. We also announced a significant and accretive acquisition in our core area of the U.K. North Sea,” said William L. Transier, chairman, chief executive officer and president. “During 2012, we will stay focused on activities designed to increase our U.K. North Sea crude and natural gas production.”

Operational Update

United Kingdom

In December, Endeavour announced the acquisition of interests in three producing oil fields in the North Sea. Current net production from the group of assets is approximately 10,000 boepd of Brent oil and estimated 2P reserves as of December 31, 2011 are approximately 31 mmboe. The Company is acquiring an additional 23.43% working interest in Alba, a field where it currently owns a 2.25% working interest, a 40% working interest in and, subject to partner approval, operatorship of MacCulloch, and an 18% interest in Nicol. The transaction is expected to close in the first quarter of 2012.

At the Bacchus field in Block 22/06a in the Central North Sea, in which Endeavour holds a 30% working interest, drilling at the first of three planned production wells has reached total depth. The liner for the well has been cemented in place and preparations are being made to run the production string. The operator has announced that production is expected to begin in the first quarter of 2012.

The Rochelle development continues on schedule for first production in the fourth quarter of 2012 with the contracted drilling rig expected to arrive in the spring to commence drilling of the two planned production wells. Endeavour is operator and holds a 44% ownership interest in the Rochelle development which is comprised of Blocks 15/26b, 15/26c and 15/27.

United States Onshore

In the fourth quarter of 2011, Endeavour significantly decelerated its capital spending program in its Haynesville area. The Company currently has one Haynesville well in progress, and key acreage is held by production. Any additional Haynesville wells drilled during 2012 will be discretionary. U.S. net daily production averaged 19 MMCFe/D for the fourth quarter with the quarter exit volumes at approximately 20 MMCFe/D.

In the Heath Shale tight oil play, the Company and its partners are completing core and log data analysis from its four vertical pilot wells. Endeavour plans to define possible horizontal re-entry target zones and test the play later this year.

Other Items

Endeavour priced $500 million of Priority Notes, due 2018. The Company intends to use the net proceeds from the offering to fund its previously announced acquisition of interests in three oil fields in the United Kingdom North Sea, to repay all amounts outstanding under its Senior Term Loan due 2013 and for general corporate purposes. The transaction was completed and funded on February 23, 2012.

Endeavour’s capital expenditure budget will be between $150 million and $175 million for 2012. The Company expects to spend approximately $125 million to $150 million of the total budget in the U.K. primarily on the advancement of its key development projects – Bacchus and Rochelle. The acquisition of the three new North Sea assets would add another $20 million to $25 million to Endeavour’s planned capital budget, subsequent to the completion of the transaction.

The Company’s year-over-year proved reserve replacement rate was 423% of 2011 production. Pro forma for the announced North Sea acquisition, 2P reserves would increase to 76.0 mmboe at year-end 2011, compared to 43.7 mmboe at year-end 2010.

Earnings Conference Call, Wednesday, February 29, 2012 at 9:00 a.m., Central Time, 3:00 p.m. British Time

Endeavour International will host a conference call and web cast to discuss its 2011 year-end and fourth quarter financial and operating results on Wednesday, February 29, 2012 at 9 a.m. Central Time, 3 p.m. British Time. To participate and ask questions during the conference call, dial the local country telephone number and the confirmation code 7049567. The toll-free numbers are 888-710-3981 in the United States and 0-808-101-1402 in the United Kingdom. Other international callers should dial 913-312-1397 (tolls apply). To listen only to the live audio web cast access Endeavour’s home page at www.endeavourcorp.com. A replay will be available beginning at 12:00 p.m. Central Time on February 29, 2012 through 12:00 p.m. on March 7, 2012 by dialing toll free 888-203-1112 (U.S.) or 719-457-0820 (international), confirmation code 7049567.

Endeavour International Corporation is an oil and gas exploration and production company focused on the acquisition, exploration and development of energy reserves in the North Sea and the United States. For more information, visit www.endeavourcorp.com.

Additional Information for Investors:

Certain statements in this news release should be regarded as “forward-looking” statements within the meaning of the securities laws. These statements speak only as of the date made. Such statements are subject to assumptions, risk and uncertainty. Actual results or events may vary materially.

As of January 1, 2010, the Securities and Exchange Commission (SEC) changed its rules to permit oil and gas companies, in their filings with the SEC, to disclose not only proved reserves, but also probable reserves and possible reserves. Proved oil and gas reserves are those quantities of oil and gas, which, by analysis of geosciences and engineering data, can be estimated with reasonable certainty to be economically producible — from a given date forward, from known reservoirs, and under existing economic conditions, operating methods, and government regulations — prior to the time at which contracts providing the right to operate expire. Probable reserves include those additional reserves that a company believes are as likely as not to be recovered and possible reserves include those additional reserves that are less certain to be recovered than probable reserves. We use may use certain terms in our news releases, such as “reserve potential,” that the SEC’s guidelines strictly prohibit us from including in filings with the SEC. We note that the SEC also prohibits companies from aggregating proved and probable reserves in filings with the SEC due to the different level of certainty associated with each reserve category. In addition, we do not represent that the probable or possible reserves described herein meet the recoverability thresholds established by the SEC in its new definitions. Investors are urged to also consider closely the disclosure in our filings with the SEC, available from our website at www.endeavourcorp.com. Endeavour is also subject to the requirements of the London Stock Exchange and considers the disclosures in this release to be appropriate and/or required under the guidelines of that exchange.

For further information:

Endeavour International Corporation

Condensed Consolidated Balance Sheets

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Endeavour International Corporation

Condensed Consolidated Statement of Operations

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Endeavour International Corporation

Condensed Consolidated Statement of Cash Flows

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Endeavour International Corporation

Operating Statistics

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Endeavour International Corporation

Reconciliation of GAAP to Non-GAAP Measures

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As required under Regulation G of the Securities Exchange Act of 1934, provided below are reconciliations of net income (loss) to the following non-GAAP financial measures: net income, as adjusted and Adjusted EBITDA. We use these non-GAAP measures as key metrics for our management and to demonstrate our ability to internally fund capital expenditures and service debt. The non-GAAP measures are useful in comparisons of oil and gas exploration and production companies as they exclude non-operating fluctuations in assets and liabilities.