Initiating Engineering Study to Implement Long Term Test and Bring New Oil to MarketCALGARY, May 28, 2013 /PRNewswire/ - Gran Tierra Energy Inc. ("Gran Tierra Energy") (NYSE MKT: GTE, TSX: GTE), a company focused on oil exploration and production in South America, today provided updates for its exploration drilling in Peru. "Gran Tierra Energy has successfully completed testing of the sidetrack on the Bretaña Norte 95-2-1XD exploration well in Peru, with results supporting the significant potential production additions expected from the Bretaña field," said Dana Coffield, President and Chief Executive Officer of Gran Tierra Energy. "After joining Canadian Prime Minister Stephen Harper during last week's trade envoy to Peru and Colombia, I am further encouraged by Gran Tierra Energy's commitment to the vast potential in Peru. This discovery has material contingent resource potential, and is expected to provide significant growth for the company and assist Perupetro in achieving its objectives to bring new oil to the market on behalf of the Government of Peru," concluded Coffield. PeruBlock 95 (100% working interest and operator) Gran Tierra Energy completed initial testing of the Vivian Formation sandstone reservoir in the horizontal sidetrack of the Bretaña Norte 95-2-1XD exploration well. Log interpretation of the 1,595 foot sidetrack indicates the presence of an oil-bearing sandstone reservoir in the Vivian Formation beginning at 10,735 feet measured depth (" MD") to 12,262 feet MD, with a total net pay in the lateral section of 1,283 feet with an average porosity of 22.8%. A production test was conducted over the 1,595 foot horizontal length of the sidetrack penetrating approximately 25 vertical feet of the top of the Vivian Formation in the Bretaña structure. A final rate of approximately 1,699 barrels of oil per day (" BOPD") was produced on natural flow with 0% water cut, through a 32/64 inch choke. The choke size was then increased to a 64/64 inch and the oil flow increased to approximately 3,095 BOPD on natural flow with 0% water cut. Wellhead flowing pressure was increasing during the first test indicating the formation was cleaning up. Cumulative production for both testing periods was approximately 3,552 barrels of oil and testing was concluded when available storage capacity had been achieved. Detailed analysis of the test results is currently under way. The long-term test is expected to commence in the first quarter of 2014, subject to facilities upgrade, and execution of crude oil transportation and delivery agreements, at an estimated rate between 2,500 and 3,000 BOPD. Gran Tierra Energy is planning a front-end engineering and design study to assist in the expected development of the Bretaña field. Test crude is expected to be sold to the Iquitos refinery during the initial test period, one of several crude monetization options under evaluation for Bretaña.