Abstract The Luling oil field, in Caldwell and Guadalupe counties, Texas, is on a fault structure about 20 miles southeast of the main Balcones fault. The area is drained by San Marcos River. The Wilcox formation is exposed at the surface and the producing formation is the Edwards limestone of the Comanchean Cretaceous. The field is 7.5 miles long and averages about 0.5 mile wide. The discovery well was brought in on August r4, 1922. On December 31, 1926, there were 502 producing wells in the field. The structure is a faulted monocline limited on the northwest, northeast, and southwest by faults of about 450 feet displacement. The strike of the structure is northeast. The average heave of the fault measured on the top of the Edwards is about 1,400 feet. The highest points of the structure are near the two extremities of the field, the middle portion being about 40 feet lower. The sedimentary column overlies a metamorphic basement composed of rocks of pre-Comanchean or possibly pre-Cam-brian age. The average depth of the top of the Edwards oil horizon is about 2,100 feet. The oil has a gravity of about 270 Be. The total production of the field to December 31, 1926, was about 31,672,000 barrels, and the daily production about 18,900 barrels.