Growth in Market Capitalization Results in Index Listing CALGARY, Alberta, June 19 /PRNewswire-FirstCall/ -- Gran Tierra Energy Inc. (Amex: GTE; TSX: GTE), a company focused on oil exploration and production in South America, today announced that it is set to join the broad-market Russell 3000(R) Index when Russell Investments reconstitutes its comprehensive set of U.S. and global equity indexes on June 27, according to a preliminary list of additions posted June 13 on http://www.russell.com/. Commenting on the matter, Dana Coffield, President and Chief Executive Officer of Gran Tierra Energy Inc. stated, "Inclusion in the Russell 3000(R) Index reflects the success of our Company. Our oil exploration and development programs have resulted in reserves, production and cash flow growth over the last year and a half, resulting in a material growth in our market capitalization during that period." Annual reconstitution of Russell's U.S. indexes captures the 4,000 largest U.S. stocks as of the end of May, ranking them by total market capitalization. Membership in the Russell 3000, which remains in place for one year, means automatic inclusion in the large-cap Russell 1000(R) Index or small-cap Russell 2000(R) Index as well as the appropriate growth and value style indexes. Russell determines membership for its equity indexes primarily by objective, market-capitalization rankings and style attributes. The Russell 3000 also serves as the U.S. component to the Russell Global Index, which Russell launched last year. Russell indexes are widely used by investment managers and institutional investors for index funds and as benchmarks for both passive and active investment strategies. An industry-leading $4.4 trillion in assets currently are benchmarked to them. These investment tools originated from Russell's multi-manager investment business in the early 1980s when the company saw the need for a more objective, market-driven set of benchmarks in order to evaluate outside investment managers. About Gran Tierra Energy Inc.: Gran Tierra Energy Inc. is an international oil and gas exploration and production company operating in South America, headquartered in Calgary, Canada, incorporated in the United States, and trading on the American Stock Exchange (GTE) and the Toronto Stock Exchange (GTE). The company holds interests in producing and prospective properties in Argentina, Colombia and Peru. The company has a strategy that focuses on growing a portfolio of producing properties, plus production enhancement and exploration opportunities to provide a base for future growth. Additional information concerning Gran Tierra Energy is available at http://www.grantierra.com/. Investor inquiries may be directed to or 1-800-916-GTRE (4873). Contacts: Dana Coffield Al Palombo Gran Tierra Energy, Inc. Cameron Associates President & Chief Executive Officer Investor Relations (800) 916-4873 (212) 245-8800 Ext. 209 DATASOURCE: Gran Tierra Energy Inc. CONTACT: Dana Coffield, President & Chief Executive Officer of Gran Tierra Energy, Inc., 1-800-916-4873, ; or Investor Relations, Al Palombo of Cameron Associates, +1-212-245-8800, ext. 209, , for Gran Tierra Energy Inc. Web site: http://www.grantierra.com/ http://www.russell.com/

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