Gran Tierra Initiates Testing of Oil Discovery at Costayaco-1 in Colombia

    Six Drill-Stem Tests To Evaluate Four Different Reservoir Packages

    CALGARY, Alberta, June 12 /CNW/ -- Gran Tierra Energy Inc. (OTC Bulletin
Board: GTRE), a company focused on oil exploration and production in South
America, today announced that it has initiated a drill stem test (DST) program
on its recently drilled Costayaco-1 exploration well in the Chaza Block,
Putumayo Basin, in southern Colombia.
    Oil shows were encountered in four different reservoir packages during
the drilling of the well.  Oil saturations were subsequently confirmed by
electric logging.  The zones being tested include (from the lower to upper
zones) the Caballos sandstone, T sandstone, U sandstone, and Kg sandstone. 
The well has been cased and approximately 155 feet of reservoir section will
be perforated in the six DSTs.  The DST program is expected to last
approximately six weeks.
    These reservoirs are the same reservoirs that were recently tested in the
Juanambu-1 exploration well in the adjacent Guayuyaco Block, for which an
application for commerciality is currently under preparation, and are the same
reservoirs that are producing oil in adjacent oil fields operated by Gran
Tierra Energy.
    Gran Tierra Energy holds a 50% working interest and is the Operator of
the Chaza Block.  Solana Resources Limited holds the remaining 50% working
interest.  The Chaza Block is subject to the new and fiscally attractive
Agencia Nacional de Hidrocarburos royalty/tax contract which includes no
additional state participation.
    Dana Coffield, President and CEO stated "The initiation of testing in
Costayaco-1 is another milestone in the continuation of the ongoing success of
our 2007 drilling campaign.  This is our second exploration well in the
Putumayo Basin to encounter hydrocarbons this year and, like Juanambu-1, is
located near infrastructure operated by Gran Tierra Energy which should enable
rapid initiation of production if we are able to successfully complete testing
at commercial rates."

    About Gran Tierra Energy Inc.
    Gran Tierra Energy Inc. is an international oil and gas exploration and
production company, headquartered in Calgary, Canada, incorporated and traded
in the United States and operating in South America.  Gran Tierra holds
interests in producing and prospective properties in Argentina, Colombia and
Peru.  To date, Gran Tierra has pursued a strategy that focuses on
establishing a selective portfolio of producing properties and exploration
opportunities to provide a base for future growth. Additional information
concerning Gran Tierra is available at  Investor
inquiries may be directed to or 1-800-916-GTRE (4873).

    Forward Looking Statements
    The statements in this press release regarding the planned testing of the
oil discovery at Costayaco-1 exploration well and the ability to begin
production if testing is successfully completed are 'forward-looking
statements' within the meaning of Section 27A of the Securities Act of 1933,
as amended, and Section 21E of the Securities Exchange Act of 1934.  Although
these forward-looking statements reflect the good faith judgment of
management, forward-looking statements are inherently subject to known and
unknown risks and uncertainties that may cause actual results to be materially
different from those discussed in these forward-looking statements including,
but not limited to, in the case of these forward-looking statements, actual
production deviating from test results, mechanical problems, equipment
limitations and weather conditions, which could delay or prevent the
completion of the testing or the commencement of production if testing is
successfully completed.  Readers are urged not to place undue reliance on
these forward-looking statements, which speak only as of the date of this
release. Gran Tierra Energy assumes no obligation to update these
forward-looking statements in order to reflect any event or circumstance that
may arise after the date of this release, other than as may be required by
applicable law or regulation.  Readers are urged to carefully review and
consider the various disclosures, including the risk factors, made by Gran
Tierra Energy in its reports filed with the Securities and Exchange
Commission, in particular under the caption "Item 1A. Risk Factors" in its
quarterly report on Form 10-Q filed on May 15, 2007, which attempt to advise
interested parties of the risks and factors that may affect Gran Tierra's
business. If one or more of these risks or uncertainties materialize, or if
the underlying assumptions prove incorrect, Gran Tierra's actual results may
vary materially from those expected or projected.

For further information:

For further information: Dana Coffield, President & Chief Executive 
Officer of Gran Tierra Energy, Inc., 1-800-916-4873,; or 
Al Palombo, Investor Relations of Cameron Associates, +1-212-245-8800 ext.
209,, for Gran Tierra Energy, Inc. Web Site:

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