Lower Cretaceous sedimentary rocks probably underlie most of the western Gulf basin, though they are deeply buried in much of the area and have not been penetrated by wells. Average thickness of strata in the productive and prospective belts is about 4,000 ft (1,220 m); the area is 177,000 sq mi (458,430 sq km), and the volume of sedimentary rock is approximately 130,000 cu mi (541,700 cu km). A nonprospective belt, with an area of 86,000 sq mi (222,740 sq km) and a sedimentary-rock volume of about 40,000 cu mi (166,680 cu km), is updip from the proved belt. A speculative zone, which extends basinward from the prospective belt to the outer edge of the continental shelf, has an area of 77,000 sq mi (199,430 sq km); its sedimentary-rock volume may be more than 50,000 cu mi 208,350 cu km).

The sedimentary section is composed of carbonate and terrigenous clastic rocks; much of the sediment was deposited in environments favorable for the generation and accumulation of oil and gas. Approximately 300 fields in Texas, Louisiana, Arkansas, Mississippi, and Alabama have produced about 1.5 billion bbl of oil and 10.5 trillion cu ft of gas from Lower Cretaceous sandstone and carbonate rocks. The ultimate recovery from the fields and their extensions, and from new discoveries within the productive belt, will be more than double the amount already produced. In the more seaward, unexplored province, especially in the Mississippi and Rio Grande embayments and in the East Texas basin, numerous accumulations will be found in limestone reefs, shell mounds, porous dolomite, and deltaic andstone. The petroleum potential of the thick and widespread Lower Cretaceous in the western Gulf Coast is very great.