This guidebook, Hydrogeology of Trans-Pecos Texas, grew out of our interest in the hydrogeology of desert environments.

Petroleum reservoirs typically yield only a fraction of the oil initially in place because geologic heterogeneity causes incomplete drainage of oil.

Occurrences of ground-water and soil salinization are numerous in the Concho River watershed and its confluence with the Colorado River in West Texas and in other semiarid regions of Texas and the United States.

Reservoirs in the Permian Basin of Texas are estimated to have contained a total of 105.7 billion barrels (Bbbl) of oil at discovery. As of January 1985, these reservoirs had produced a cumulative volume of 25.3 Bbbl of oil, and proved reserves were calculated at 5.9 Bbbl.

The State-owned submerged lands of Texas encompass almost 6,000 mi2 (15,540 km2). They lie below waters of the bay-estuary-lagoon system and the Gulf of Mexico and extend 10.3 mi (16.6 km) seaward from the Gulf shoreline (fig. 1).