Gran Tierra Announces Initial Test Results At Costayaco-1 In Colombia

    Initial 3 Zones Flow Up To 3,997 Barrels of Oil Per Day; Three Additional
    Zones To Be Tested

    CALGARY, Alberta, June 20 /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 successfully completed three drill stem
tests (DST) on its recently drilled Costayaco-1 exploration well in the Chaza
Block, Putumayo Basin, in southern Colombia.
    The cased hole DST program commenced on June 10, 2007.  Six DSTs have
been scheduled over the Lower Caballos Formation, Middle Caballos Formation,
Lower and Middle Villeta T Formations, the Villeta U Formation, and the
Rumiyaco Kg Formation.  Three DSTs have now been completed in the lower three
zones. Production at a combined natural flow rate of up to 3,997 barrels of
oil per day (bopd) of 30 degree to 31 degree API oil was obtained in the three
formations tested to date.  Three additional DSTs over three additional zones
are scheduled.
    DST-1 tested an 8 foot thick sandstone interval in the Lower Caballos
Formation to test a potential oil-water contact.  After initial swabbing the
well started to flow naturally, reaching a maximum oil rate of 206 barrels of
oil per day (bopd) with only a trace of water.  A preliminary review of DST-1
indicates no evidence of an oil-water contact.
    DST-2 tested a 95 foot thick sequence of sandstones in the Lower and
Middle Caballos Formations, including the Lower Caballos zone perforated in
DST-1.  After one swab the well started to flow naturally, reaching a maximum
oil rate of 2,655 bopd with only a trace of water.
    DST-3 tested another potential oil water contact within a 12 foot
sandstone interval in the Lower Villeta T Formation.   After swabbing, the
well started to flow naturally, reaching a maximum oil rate of 1,342 bopd with
only a trace of water.
    Testing will continue with DST-4 in the overlying main Villeta T
Formation and then two additional DSTs will be conducted in the Villeta U and
the Rumiyaco Kg Formations.  Initial log interpretations, combined with
hydrocarbon shows encountered during drilling, indicate oil bearing reservoir
quality sandstones in these zones.  Additionally, these zones are productive
in the nearby Santana Block, as well as in the recently tested Juanambu-1
discovery well located on the adjacent Guayuyaco block operated by Gran Tierra
    Planning for a potential field development has been initiated. The Pride-
17 drilling rig, used to drill Costayaco-1, is under contract and available to
conduct additional delineation and development drilling. To optimize
positioning of future drilling locations, a new seismic acquisition program
over the Costayaco structure is being considered. Costayaco-1 is proximal to
infrastructure allowing for early monetization of commercial production.
    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, "These initial test results are
extraordinary and greatly exceeded our expectations.  The initial reservoir
performance tested to date is far superior to any of our existing assets in

    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 portfolio of producing properties, development and exploration
opportunities, through selective acquisitions, 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 future testing and
potential development of the Costayaco-1 exploration well are 'forward-looking
statements' within the meaning of Section 27A of the United States Securities
Act of 1933, as amended, and Section 21E of the United States 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 the initial test
results.  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
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 in its reports filed with the
Securities and Exchange Commission, in particular 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, Gran Tierra Energy, Inc., 
President & Chief Executive Officer, 800-916-4873, or, or 
Al Palombo, Cameron Associates, Investor Relations, 212-245-8800, ext. 209, or Web Site:

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