Gran Tierra Energy Completes Logging Operations and Initiates Production Testing of Costayaco-8

    Production Returns to Target Levels in the Putumayo Basin, Colombia

    CALGARY, June 29 /CNW/ - Gran Tierra Energy Inc. (AMEX: GTE; TSX: GTE), a
company focused on oil exploration and production in South America, today
announced that it has completed logging operations and initiated production
testing of Costayaco-8. Well logs indicate that both the Upper T Sandstone of
the Villeta formation and the Caballos formation lie completely within the
field's oil column. In addition, the Company also reported that production has
returned to target levels of between 14,000 and 16,000 barrels of oil per day
(BOPD) net after royalty following recent pipeline repairs.
    "The Upper T Sandstone and the Caballos reservoirs came in as expected
and are well above the oil/water contact for the field according to well
logs," said Dana Coffield, President and Chief Executive Officer of Gran
Tierra Energy. "Costayaco-8 was drilled on the crest of the Costayaco Field
and early indications suggest the well will be a significant contributor to
the production potential of the field."
    Costayaco-8, located 1,868 feet southwest of Costayaco-1, reached a total
measured depth (MD) of 8,570 feet on June 20, 2009. Well logs indicate the
presence of reservoir sandstones in the Upper T Sandstone from 8,142 feet MD
to 8,198 feet MD and in the Caballos formation from 8,268 feet MD to 8,437
feet MD. The bottom of both formations came in above their respective
oil/water contacts. The gross reservoir thicknesses of the Upper T Sandstone
and the Caballos formation are 56 feet and 169 feet respectively.
    During drilling operations, Gran Tierra Energy successfully acquired
cores of the major sandstone reservoir intervals in Upper T Sandstone and the
Caballos formation. These cores will be used to further assess reservoir
parameters, including oil saturations of both zones.
    Completion and production testing operations at Costayaco-8 have been
initiated and are expected to take approximately two weeks. Testing of
Costayaco-7 is continuing and anticipated to be complete in early July.
    Once initial production testing is completed at Costayaco-8 the drilling
rig will be moved to the Costayaco-9 site, located 1,958 feet southwest of
Costayaco-8. Site preparation for Costayaco-9 is currently underway, and
drilling is expected to begin in early July.
    The Costayaco field is located in the Chaza Block in the Putumayo Basin
of Colombia, where the company has a 100% working interest and is the
operator.

    Production Update

    Following repairs to the Ecopetrol-operated Trans Andean Pipeline, normal
production operations have resumed and are currently averaging approximately
17,800 BOPD gross, or 14,750 BOPD net after royalty in Colombia. During the 15
days of reduced production due to pipeline repairs, oil sales averaged
approximately 3,610 BOPD gross or 2,963 BOPD net after royalty.
    Production in Argentina averaged approximately 694 BOPD net after royalty
in June due to the temporary shut-in of four wells for workovers.

    About Gran Tierra Energy Inc.

    Gran Tierra Energy Inc. is an international oil and gas exploration and
production company, headquartered in Calgary, Canada, incorporated in the
United States, trading on the NYSE Amex Exchange (GTE) and the Toronto Stock
Exchange (GTE), and operating in South America. Gran Tierra Energy holds
interests in producing and prospective properties in Argentina, Colombia and
Peru. Gran Tierra Energy has a strategy that focuses on establishing a
portfolio of producing properties, plus production enhancement and exploration
opportunities to provide a base for future growth. Additional information
concerning Gran Tierra Energy is available at www.grantierra.com.

    Forward Looking Statements:

    The statements in this news release regarding early indications that
Costayaco-8 will be a significant contributor to production potential of the
field, and Gran Tierra Energy's expectations regarding the expected timing for
completion of testing of Costayaco-7, Costayaco-8, and the beginning of
drilling operations on Costayaco-9, are forward looking statements or
financial outlook ("forward-looking statements") under the meaning of
applicable securities laws, including Canadian Securities Administrators'
National Instrument 51-102 Continuous Disclosure Obligations and the United
States Private Securities Litigation Reform Act of 1995. These statements are
subject to risks, uncertainties and other factors that could cause actual
results or outcomes to differ materially from those contemplated by the
forward-looking statements. There are a number of important factors that could
cause the actual results or outcomes to differ materially from those indicated
by the forward-looking statements, including, among others: Gran Tierra
Energy's operations are located in South America, and unexpected problems can
arise due to guerilla activity, technical difficulties and operational
difficulties which impact its testing, drilling and production operations, and
transport or sale of its products; and geographic, political and weather
conditions can impact testing, drilling and production operations, and the
production, transport or sale of its products. Further information on
potential factors that could affect Gran Tierra Energy are included in risks
detailed from time to time in Gran Tierra Energy's Securities and Exchange
Commission filings, including, without limitation, under the caption "Risk
Factors" in Gran Tierra Energy's Quarterly Report on Form 10-Q filed May 8,
2009. These filings are available on a Web site maintained by the Securities
and Exchange Commission at http://www.sec.gov and on SEDAR at www.sedar.com.
The forward-looking statements contained herein are expressly qualified in
their entirety by this cautionary statement. The forward-looking statements
are made as of the date of this press release and Gran Tierra Energy disclaims
any intention or obligation to update or revise the forward-looking
statements, whether as a result of new information, future events or
otherwise, except as expressly required by applicable securities legislation.

For further information: For media and investor inquiries please contact
Thomas McMillan, Equicom Group, (866) 973-4873, (403) 536-5903,
info@grantierra.com

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