Texas has long been a major oil province, accounting for nearly 40 percent of the historic production of crude oil in the United States. Texas now holds less than 30 percent of the Nation's proven reserves and less than 15 percent of its estimated as-yet-undiscovered oil. Discovery and conventional production of oil in Texas have peaked, but more than 100 billion barrels of oil now classed largely as unrecoverable still exist in Texas. This oil, even with the geologic, technical, and economic constraints on its recovery, constitutes a major target for future production.

The Nacatoch Formation of the East Texas Basin is the middle formation of the Navarro Group and consists of marine sandstones and mudstones derived largely from source areas to the northwest, north, and northeast of the East Texas Embayment. Terrigenous clastics were supplied to the Nacatoch Basin by a major northeastern dispersal system originating in southwest Arkansas. Three minor fluvial-delta systems contributed sediment in southern Red River, Delta, and Hunt Counties, Texas.

Continuity of sandstone reservoirs is controlled by various factors, including faults, sand-body geometry, and the distribution of framework grains, matrices, and interstices within the sand body. Except for faults, these factors are largely inherited from the depositional environment and modified during sandstone compaction and cementation.

Lignite deeper than 200 ft (61 m) constitutes about 60 percent of the total lignite resources in Texas. Projections indicate that meeting future demand will require mining this deep-basin lignite. However, because the principal lignite host, the Eocene Wilcox Group, is also a major fresh-water aquifer, deep-basin lignite development by surface mining or underground gasification poses unanswered questions concerning hydrogeologic feasibility and environmental impacts.

A three-dimensional model was constructed of ground-water flow in the Wilcox-Carrizo aquifer system near Oakwood salt dome to facilitate understanding the hydrogeology around salt domes of the Gulf interior region and ultimately to evaluate the hydrologic suitability of Oakwood Dome for storage of high-level nuclear waste. The data base includes not only measurements of hydraulic head and hydraulic conductivity but also lithofacies maps constructed in a previous study of Wilcox depositional systems.