Mexico's growing oil production is all that has kept its economy viable. The first oil well in Mexico was drilled in 1869 near the Furbero seeps in Vera Cruz. The Burgos basin in northeastern Mexico has accounted for substantial petroleum production. With production averaging 2.79 million barrels per day, Mexico would have produced 1.018 billion barrels of oil in 1981. By 1921 Mexico accounted for 25 percent of world oil production. Some of the wells, particularly those in Cerro Azul, produced tremendous flows of oil. The Reforma-Campeche area accounts for about 87 percent of Mexico's total oil production and contains by far the best prospects for additional oil discoveries. The Reforma-Campeche reservoirs are late Mesozoic and early Cenozoic giant reef atolls and banks formed in an open downwarped extracontmental basin. Mexico possesses a very significant petroleum reserve and excellent prospects for large additional discoveries.