CALGARY, Canada, November 20, 2007 - Gran Tierra Energy Inc. (OTC Bulletin Board: GTRE), a company focused on oil exploration and production in South America, today announced that the company has received approval of commerciality for the Juanambu oil field in the Guayuyaco Block in Colombia. Production from this new oil field has been established at approximately 1,410 barrels of oil per day.

Gran Tierra Energy discovered the Juanambu oil field in the Putumayo Basin of southern Colombia in the first quarter of 2007 with the Juanambu-1 exploration well. The company subsequently undertook testing of this well in the second quarter of 2007, and applied for commerciality to Ecopetrol, the national oil and gas company of Colombia, in the third quarter of 2007. Gran Tierra Energy has now obtained approval of commerciality from Ecopetrol.

The Guayuyaco Block is governed by an Association Contract. Under the terms of the Association Contract Ecopetrol has the right to back into the Juanambu oil field for a 30% interest upon declaration of commerciality. Gran Tierra Energy now holds a 35% interest in the Juanambu field and will retain Operatorship of both the field and the Guayuyaco Block. Solana Resources also retains a 35% interest in the field.

Production of the 32 degree API quality crude is currently being transported by truck. A five kilometer six inch flow-line is being planned to transport oil from the Juanambu-1 discovery well to existing infrastructure. Construction of this line is scheduled to begin in mid-December, 2007, and is scheduled to be completed in mid-January, 2008.

Gran Tierra Energy's production in Colombia has been averaging approximately 1,500 BOPD, net after royalty, and production from operations in Argentina has been averaging approximately 600 BOPD, net after royalty. With this new production from Juanambu, Gran Tierra Energy's net after royalty average production is now approximately 2,600 BOPD, compared to an average production of approximately 2,100 BOPD average since September of 2007.

Dana Coffield, President and CEO, stated "Gran Tierra Energy has been experiencing sustained production growth in the second half of 2007 as we initiated trucking operations to handle new production from our oil discoveries made in the first half of 2007. The bulk of our capital program for 2008 will be dedicated to continuing the development of these reserves, both by development drilling and building associated production infrastructure. This is an extremely exciting time in the growth of Gran Tierra Energy as we transition from an exploration focused company to a development focused company that will be growing production while executing ongoing exploration programs to build on our reserve base."

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 Energy holds interests in producing and prospective properties in Argentina, Colombia and Peru. The company strategy is focused on establishing a portfolio of drilling opportunities to exploit undeveloped reserves to grow production, as well as undertaking exploration to grow future reserves. Additional information concerning Gran Tierra Energy is available at www.grantierra.com. Investor inquiries may be directed to [email protected] or 1-800-916-GTRE (4873).

Forward Looking Statements

The statements in this press release regarding Gran Tierra Energy's expectations regarding the timing of construction of the pipeline from the Juanambu-1 discovery well to existing infrastructure, that the bulk of its capital program for 2008 will be dedicated to continuing the development of reserves, both by development drilling and building associated production infrastructure, and that it will be transitioning to a development focused company that will be growing production while executing ongoing exploration programs to build on its reserve base, 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, unexpected delays in drilling or pipeline or other transportation infrastructure completion due to equipment failure or other unforeseen reasons; unforeseen events, such as unexpected difficulties in drilling or unexpected discoveries, may cause Gran Tierra Energy to reallocate resources, which may delay drilling, surveys, design plans, transportation infrastructure development and production or alter the mix of development drilling and exploration drilling in Gran Tierra Energy's portfolio; and unexpected costs may decrease funds available to carry out Gran Tierra Energy's plans described in the press release, which could delay or prevent execution of these plans. 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 Energy in its reports filed with the Securities and Exchange Commission, in particular its quarterly report on Form 10-Q filed on November 8, 2007, which attempt to advise interested parties of the risks and factors that may affect Gran Tierra Energy's business. If one or more of these risks or uncertainties materialize, or if the underlying assumptions prove incorrect, Gran Tierra Energy's actual results may vary materially from those expected or projected.