The O'Hern field is located in a downthrown fault block on the southeast flank of the Cole-Bruni anticline in Duval and Webb counties, 42 miles east of Laredo, Texas. The O'Hern sand occurs in the geologic column near the contact of the Jackson and Cockfield-Yegua formations. It was deposited in the O'Hern field area in the form of a landward-pointed tongue, the edge of which forms three-fourths of the boundary of production above the oil-water contact. The O'Hern field had produced nearly 8 million barrels of oil on January 1, 1940. The peak of production came in September, 1937. Most of the wells flowed on completion although there was no evident gas cap in the field. There was a gradual shrinkage of the areas containing flowing wells over a period of about 4 years and he field was composed almost entirely of pumping wells by January 1, 1940. The field has certain peculiarities in the pattern of production. These include: (1) a marginal zone in which all oil wells were pumping wells on completion, even in the early stages of development; (2) a number of gas wells widely distributed as to structural position but restricted to the marginal zone of pumping wells; and (3) a transverse band of subnormal production across the central part of the field. These peculiarities in the pattern of production are interpreted as being a direct result of characteristics in the corresponding pattern of deposition of the O'Hern sand.