Oil and gas resources in crystalline igneous and metamorphic reservoirs are well documented globally and in Texas. More than 190 oil and gas fields and accumulations with recoverable hydrocarbons in “basement” igneous and metamorphic rocks or volcanogenic extrusive and intrusive rocks around the world have been documented in published literature and unpublished company reports.

Proterozoic exposures in the Llano Uplift of Central Texas and in the Van Horn area and other smaller areas of western Texas represent less than one percent of the area underlain by Precambrian basement. The geologic units of the Llano Uplift are dominated by felsic gneiss (34 percent), schist (26 percent), and granite (39 percent) that formed during the Mesoproterozoic Grenville orogeny. These lithologies likely form a significant component of the contiguous Texas basement under Phanerozoic strata.