Gran Tierra Energy Announces Oil Discovery With 2,324 BOPD Test Rate in Argentina

    Exploration Success Adds Near-Term Production and Cash Flow to Argentine
    Business Unit; Increases Exploration Potential of Acreage

    CALGARY, Alberta, Sept. 17 /CNW/ -- Gran Tierra Energy Inc. (Amex:   GTE;
TSX: GTE), a company focused on oil exploration and production in South
America, today announced it has finished drilling and testing the Proa.x-1
exploration well in the Surubi Block, Noroeste Basin, Argentina.
    Gran Tierra Energy began drilling the Proa.x-1 exploration well on July
9, 2008 and reached total measured depth of 12,920 feet on August 28, 2008. 
Good oil shows were encountered in Cretaceous volcanics and volcaniclastics in
the Palmar Largo Formation during drilling and oil saturations were indicated
on logs.  Gran Tierra Energy conducted a drill-stem test in the Lower Palmar
Largo formation from 12,694 to 12,713 feet and obtained no flow.  The company
then conducted a production test in the intervals 12,649 to 12,661 feet and
12,620 to 12,641 feet, and obtained a stabilized gross flow rate of 2,324
barrels of oil per day (BOPD) through a 35/64 inch choke with a watercut of
0.5 percent.  The oil gravity was 43.8 degree API at 60 degree Fahrenheit.
    Gran Tierra Energy will initiate long-term production testing in
approximately one week, with commercial oil sales to begin concurrently. Crude
oil transportation will be through an existing 3-1/2 inch, 15 kilometer
pipeline with approximately 4,000 BOPD capacity to existing facilities at the
Gran Tierra Energy-operated Chivil field in the adjacent Chivil Block.  Gran
Tierra Energy oil production in Argentina has been averaging approximately 570
BOPD net after royalty to date in the third quarter of 2008.
    Gran Tierra Energy is the operator and has an 85% working interest in the
90,688 gross acre Surubi Block in the Formosa Province in northern Argentina.
REFSA (Recursos Energeticos Formosa S.A.), the provincial government company
has a 15% working interest. REFSA's costs were carried by Gran Tierra Energy
during drilling of the Proa.x-1 well. Gran Tierra Energy will be reimbursed
for all costs incurred during drilling from 50% of the net production assigned
to REFSA. The provincial royalties payable on production in the revised
contract vary from 12% for cumulative production below 750,000 cubic meters of
oil (approximately 4.7 million barrels of oil), to 14% for cumulative
production between 750,000 to 1,500,000 cubic meters of oil (approximately 9.4
million barrels of oil), and to 16% for cumulative production above 1,500,000
cubic meters of oil.
    Commenting on the drilling and testing progress, Dana Coffield, President
and Chief Executive Officer of Gran Tierra Energy Inc., stated, "The Proa.x-1
test results should prove to be a substantial reserves and production addition
to our Argentine business unit.  This success adds near-term production and
cash flow to our Argentina business unit, in addition to increasing the
prospectivity of identified leads in the Surubi Block and in the adjoining
Chivil and Palmar Largo Blocks, where Gran Tierra Energy has a 100% and 14%
working interest respectively."
    About Gran Tierra Energy Inc.:
    Gran Tierra Energy Inc. is an international oil and gas exploration and
production company operating in South America, headquartered in Calgary,
Canada, incorporated in the United States, and trading on the American Stock
Exchange (GTE) and the Toronto Stock Exchange (GTE). The company holds
interests in producing and prospective properties in Argentina, Colombia and
Peru. The company has a strategy that focuses on growing 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
Investor inquiries may be directed to or 1-800-916-GTRE
    Cautionary Statements:
    The statements in this news release regarding Gran Tierra Energy's plans
and expectations for reserves, production, drilling, testing, future commodity
sales, transportation, reimbursement of costs and infrastructure, including
the timing of commencement and completion of these events, are forward looking
information, forward looking statements or financial outlooks (collectively,
"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 forward-looking 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.  Although, Gran Tierra Energy believes that the assumptions
underlying, and expectations reflected in, these forward-looking statements
are reasonable, it can give no assurance that these assumptions and
expectations will prove to be correct. Important factors that could cause the
results or outcomes discussed herein to differ materially from those indicated
by these forward-looking statements include, among other things:  Gran Tierra
Energy's operations are located in South America, and unexpected problems can
arise due to technical difficulties and operational difficulties which impact
the production, transport or sale of oil and gas; and unexpected problems due
to weather conditions.  In addition, the price per barrel of oil paid to Gran
Tierra Energy by its refiner in Argentina is substantially less than the price
received by Gran Tierra Energy in Colombia and, as a result, the percentage
increase in production resulting from production in Argentina will not result
in a corresponding percentage increase in Gran Tierra Energy revenues. 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 "Item 1A -- Risk Factors" in Part II of Gran Tierra Energy's
Quarterly Report on Form 10-Q for the period ended June 30, 2008, filed with
the Securities and Exchange Commission on August 11, 2008.  These filings are
available on a Web site maintained by the Securities and Exchange Commission
at The forward-looking statements contained herein are
made as at the date of this press release. Subject to its obligations under
applicable law, Gran Tierra Energy does not undertake an obligation to update
forward-looking or other statements in this release. Gran Tierra Energy's
forward-looking statements are expressly qualified in their entirety by this
cautionary statement.


      Dana Coffield                             Al Palombo
      Gran Tierra Energy, Inc.                  Cameron Associates
      President & Chief Executive Officer       Investor Relations
      1-800-916-4873                            +1-212-554-5488             


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, +1-212-554-5488,, for Gran Tierra Energy Inc. Web Site:

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