The Permian basin of west Texas and southeast New Mexico remains an important oil-producing province, accounting for 17% of United States production (327 million bbl) in 2002. With a resource base of such size, increased understanding of reservoir geology and improved use of enhanced-recovery practices in the basin can have a substantial impact on United States oil production. Thirty-two oil plays covering both the Texas and New Mexico portions of the Permian basin were defined on the basis of reservoir stratigraphy, lithology, depositional environment, and structural and tectonic setting. One thousand three hundred and thirty-nine significant-sized reservoirs (cumulative production of 1 million bbl [1.59 10⁵ m³] of oil through 2000) were assigned to a geologic play. Cumulative production from these reservoirs was 28.9 billion bbl (4.59 10⁹ m³), or 95% of the basin's total. Examples of successful reservoir-development practices are listed by play because methods demonstrated to work well in one reservoir should be applicable to other reservoirs in the play.

The Permian basin is dominantly a carbonate province. Carbonate reservoirs account for 75% of total oil production; clastics, 14%; mixed clastics and carbonates, 8%; and chert, 3%. The plays having the largest cumulative production are the Northwest shelf San Andres platform carbonate play (4.0 billion bbl; 6.31 10⁸ m³), the Leonard restricted platform carbonate play (3.3 billion bbl; 5.25 10⁸ m³), the Pennsylvanian and Lower Permian Horseshoe atoll carbonate play (2.7 billion bbl; 4.29 10⁸ m³), and the San Andres platform carbonate play (2.2 billion bbl; 3.42 10⁸ m³). The Permian system dominates production, accounting for 73% of cumulative production, followed by the Pennsylvanian (13%) and the Ordovician (6%). The estimated remaining reserves from that component of the resource base that is already discovered and producing is 3.25 billion bbl (5.17 10⁸ m³).