Gran Tierra Completes Drilling Costayaco-1 Exploration Well In Colombia

Calgary, Alberta - Gran Tierra Energy Inc., a company focused on oil exploration and production in South America, recently announced that it has successfully drilled, logged and cased a new field wildcat well in the Chaza Block, Putumayo Basin, in southern Colombia. Significant hydrocarbon shows were encountered and a testing program is currently being planned.

Gran Tierra Energy holds a 50% working interest and is Operator of this block. Partner, Solana Resources Limited, holds a 50% working interest. The Chaza Block is subject to the most recent Agencia Nacional de Hidrocarburos (ANH) contract terms, with attractive fiscal terms including a sliding scale royalty commencing at 8% and no back-in rights by the state company Ecopetrol.

Gran Tierra reported that its Costayaco-1 well reached a total measured depth of 8,570 feet on May 10, 2007. The well encountered reservoir quality sandstones with oil and gas shows in four zones. Initial log interpretations indicate potential oil pay in the Kg Sand Unit of the Rumiyaco Formation, the U Sandstone Unit of the Villeta Formation, the T Sandstone Unit of the Villeta Formation and in the Caballos Formation. These are the same four zones currently undergoing drill stem tests in Gran Tierra's recent Juanambu-1 oil discovery in the adjacent Guayuyaco Block, and are proven producing reservoirs in fields in the adjacent Santana and Guayuyaco Blocks operated by Gran Tierra Energy.

The Costayaco-1 well bore has been cased in preparation for testing. The service rig currently testing Juanambu-1 will move to the Costayaco-1 location to begin testing operations in June. Planning for a seismic acquisition infill program over the Costayaco structure has been initiated to optimize potential delineation and development drilling locations.

Dana Coffield, President and Chief Executive Officer of Gran Tierra, stated, "These early positive results justify an extensive testing program to evaluate the commercial potential of the encountered hydrocarbons zones similar to those currently underway at our Juanambu-1 discovery. This has the potential to be our third oil discovery this year, following the nearby Juanambu oil well in March which is currently being tested, and the Puesto Climaco-2D oil well in Argentina in January which is currently on production."

SOURCE: Gran Tierra Energy Inc.