The Big Foot oil field is in northeast Frio County, Texas, slightly downdip from the Balcones fault trend. Discovery was based on detailed subsurface stratigraphic studies supplemented by seismic and core-test data. The field produces from a stratigraphic trap type reservoir formed by the updip pinch-out of the Upper Cretaceous Olmos sands against a southeast-dipping unconformity. The producing zone occurs at about 3,500 feet. Production is near the marginal level; wells vary from 5 to 35 barrels of oil per day.

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