Gran Tierra Energy Inc. today announced that results from the independent reserve auditors report of Gaffney, Cline & Associates (GCA) and internal assessments relating to Gran Tierra Energy’s exploration drilling program in the first half of 2007, have increased the company’s reported proved, probable, and possible reserves 361%, and have increased the company’s reported proved reserves 197%.

Dana Coffield, President and CEO, stated “Gran Tierra Energy has attained extraordinary oil reserve growth in the first half of 2007 as a result of our operated drilling activity. We believe these results affirm our strategy of acquiring underdeveloped lands and adding value by drilling. In the last two years, since inception of Gran Tierra Energy, our focus has been on identifying and acquiring underdeveloped lands; our focus in 2007 has been on developing these lands by drilling. As a result, we have now more than tripled our acquired proved, probable and possible oil reserve base and almost doubled our acquired proved oil reserve base by executing our drilling program in the first half of 2007.”

The discovery of the Costayaco field in the Chaza Block, located in the Putumayo Basin of Colombia and operated by Gran Tierra Energy, was the result of drilling the Costayaco-1 exploration well in the second quarter of 2007. GCA has evaluated the well data and associated geoscience data, and has allocated to Gran Tierra Energy proved reserves of 3.0 million barrels of oil, with additional probable reserves of 6.0 million barrels of oil, and additional possible reserves of 8.2 million barrels of oil (all net after royalty).

The discovery of the Juanambu field in the Guayuyaco Block, also located in the Putumayo Basin of Colombia and operated by Gran Tierra Energy, was the result of drilling the Juanambu-1 exploration well earlier in 2007. GCA has evaluated the well data and associated geoscience data, and has allocated to Gran Tierra Energy proved reserves of 0.1 million barrels of oil, with additional probable reserves of 0.3 million barrels of oil, and additional possible reserves of 1.1 million barrels of oil (all net after royalty).

The Puesto Climaco-2D sidetrack well in the Vinalar Block, located in the Noroeste Basin of Argentina, tested a deeper undeveloped reservoir beneath the existing Puesto Climaco field at the beginning of 2007. Gran Tierra Energy internally evaluated the well data and associated geoscience data, and has reallocated reserves associated with this well from existing proved undeveloped reserves to new proved producing reserves. This reallocation does not impact total proved reserves.