HOUSTON, April 15, 2010 /PRNewswire/ -- Endeavour International Corporation today announced successful appraisal drilling in the western area of the Cygnus gas field in block 44/11a has led to increased reserves and prospective resource estimates and extended the field boundary to the north and west. Preliminary estimates of Cygnus reserves and prospective resources could potentially be as high as 2 trillion cubic feet of gas based on new well information making Cygnus one of the largest gas fields ever discovered in the United Kingdom sector of the southern North Sea.

This significant extension of the Cygnus field allows us to develop the area with a simplified, compressed, and lower-cost development and higher initial production rates that will accelerate to peak production levels more quickly, said William L. Transier, chairman, chief executive officer and president. This very positive increase in Cygnus reserves is another indication of the underlying value of our UK portfolio of assets.

The 44/11a-4 well was drilled to a depth of 12,207 feet vertical depth subsea, encountered a high quality, gas-saturated Leman sand reservoir 54 feet high to prognosis with a sand thickness of 130 feet gross and 85 feet net. The well was flow tested at a rate of 28 million cubic feet of gas per day.

The discovery well and five appraisal wells drilled in the Cygnus field support a common field-wide gas water contact within approximately 10 feet with the exception of the 44/11-2 well in the extreme southwest.

When operations cease on this well, the rig will be mobilized to the southern part of the Cygnus field to drill a sixth well, the 44/12a-E appraisal well. The Cygnus group plans to acquire a new field-wide 3-D seismic survey covering the expanded boundaries of the field.

Endeavour holds a 12.5 percent interest in blocks 44/11a and 12a. License partners are GDF Suez EP, the operator, and Centrica.

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 United States. For more information, visit http://www.endeavourcorp.com.

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. The estimates of recoverable resources per well and completed well costs included herein are based upon other typical results in these shale plays and may not be indicative of actual results.

SOURCE: Endeavour International Corporation

CONTACT: Investor Relations, Mike Kirksey, of Endeavour, +44(0)207-451-2381, +1-713-307-8788; or UK Broker, Jeffrey Auld of CanaccordAdams, +44 (0) 207-050-6500, for Endeavour International Corporation; or UKMedia, Philip Dennis, +44 (0) 20-7337-1516, or Henry Lerwill, +44 (0)20-7337-1526, both of Pelham Bell Pottinger, for Endeavour InternationalCorporation