The Hobbs field is near the southwestern rim of the Llano Estacado. Structure can not be mapped at the surface; the field was discovered by geophysical surveys. The producing structure is an elongate dome. The oil and gas reservoirs are members of that Permian system which occupies the Permian basin of West Texas and southeastern New Mexico. The main reservoir is a porous, light-colored limestone about 200 feet thick. The pressure in this reservoir is more than 1,500 pounds per square inch at a depth of 4,150-4,200 feet. Beyond the limits of the oil pool the reservoir-rock contains water under corresponding pressure. Porosity (hence initial production) is related to structure, being greatest along the anticlinal crest, less on the flanks, least in wells off structure. App oximately one-third of the folding occurred shortly after the deposition of the main limestone reservoir and before salt deposition. Almost two-thirds occurred after salt deposition and was probably post-Triassic, certainly pre-Pliocene.