Exhibit 99.1
 
 For immediate release
 Endeavour Announces Pricing of $120 Million
Convertible Senior Notes Due 2016
 Houston, July 18, 2011 
    This press release contains forward-looking statements within the meaning of Section 27A of
the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. These
forward-looking statements include statements that




---



##### 



express a belief, expectation, or intention, as well as those that are not statements of historical
fact, and may include projections and estimates concerning the timing and success of specific
projects and our future production, revenues, income and capital spending. Our forward-looking
statements are generally accompanied by words such as estimate, project, predict, believe,
expect, anticipate, potential, plan, goal or other words that convey the uncertainty of
future events or outcomes. We caution you not to rely on them unduly. We have based these
forward-looking statements on our current expectations and assumptions about future events. While
our management considers these expectations and assumptions to be reasonable, they are inherently
subject to significant business, economic, competitive, regulatory and other risks, contingencies
and uncertainties, most of which are difficult to predict and many of which are beyond our control.
These risks, contingencies and uncertainties, which may not be exhaustive, relate to, among other
matters, the following: discovery, estimation, development and replacement of oil and gas reserves;
decreases in proved reserves due to technical or economic factors; drilling of wells and other
planned exploitation activities; timing and amount of future production of oil and gas; the
volatility of oil and gas prices; availability and terms of capital; operating costs such as lease
operating expenses, administrative costs and other expenses; our future operating or financial
results; amount, nature and timing of capital expenditures, including future development costs;
cash flow and anticipated liquidity; availability of drilling and production equipment;
uncertainties related to drilling and production operations in a new region; cost and access to
natural gas gathering, treatment and pipeline facilities; business strategy and the availability of
acquisition opportunities; and factors not known to us at this time. Any of these factors, or any
combination of these factors, could materially affect our future financial condition or results of
operations and the ultimate accuracy of a forward-looking statement. The forward-looking
statements are not guarantees of our future performance, and our actual results and future
developments may differ materially from those projected in the forward-looking statements. In
addition, any or all of our forward-looking statements included in this release may turn out to be
incorrect. They can be affected by inaccurate assumptions we might make or by known or unknown
risks and uncertainties, including those included in our Annual Report on Form 10-K for the year
ended December 31, 2010. There can be no assurance that we will complete the Marcellus
acquisition..
 Endeavour International Corporation is an international 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
 For further information:
 Endeavour  Investor Relations
 Mike KirkseyDarcey Matthews
    
    713-307-8700713-807-8711