The Westbrook oil field is doubly worthy of description because it is the discovery field of western Texas and because oil was found in Permian strata, previously not seriously considered as oil-producing beds. Since the first producer in 1920, a 10-barrel well at 2,498 feet, 77 wells have been drilled, averaging 40 barrels each. Early in 1926, 8 were producing. The Triassic extends from the surface to 500 feet in depth; the remainder of the section is Permian. Several key beds in the Permian are used to map the subsurface structure which is that of a northeast-southwest anticline. The 2,400-foot "pay" and the 3,000-foot "Morrison sand" are themselves good markers, occurring along porous zones within definite vertical limits. The productive reservoir is dolomitic limeston . The oil has a gravity of 25.8° Be., and contains 4 per cent sulphur, and 32 per cent gasoline. Its source is probably the Permian limestones and shales. Two kinds of gas occur in the field: (1) non-inflammable gas at depths between 1,000 and 1,300 feet and (2) wet petroleum gas in both oil zones.