Potential for commercial hydrocarbon accumulations in Eocene and older strata of the Duval County Ranch in South Texas was assessed using seismic data. Three seismic facies are recognized and tied to well control.

Chert reservoirs of the Lower Devonian Thirtyone Formation represent a substantial part of the hydrocarbon resource in the Permian Basin. More than 700 million barrels of oil has been produced from these rocks, and an equivalent amount of mobile oil remains.