Gran Tierra Initiates Production Testing of Costayaco-8 Onshore Colombia

Gran Tierra Energy Inc.

Gran Tierra Energy 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.