Torsion-balance work in 1934 indicated a large minimum which centered, after regional corrections were applied, slightly north of the present producing area. After two wells were drilled in the vicinity, both of which were abandoned after encouraging showings, the area was detailed with the reflection seismograph, using the continuous profile method. As the result of this work, the discovery well was located and subsequent development of the field showed that the seismograph gave a remarkably accurate picture of the structure, a faulted dome elongate east and west.

The three producing sands are the Marginulina sand with an average of 7½ feet of effective sand, the Frio No. 1 with 10 feet, and the Frio No. 2 with 5 feet. Each sand has a separate water level and oil-gas contact and all occur within an interval of about 100 feet. The average total depth of wells is 6,500 feet. The maximum producing area is expected to be about 1,200 acres. One deep test in the field failed to find any promising deeper sands. There are now 51 oil wells and two gas wells here and development is nearly complete. As of January 1, 1941, the field had produced 1,573,400 barrels.