The south Texas report includes 58 counties within Texas Railroad Commission Districts 1, 2, and 4, and portions of the Texas offshore.

Overall exploratory activity decreased 9% from 1980 totals. District 1 experienced an increase in activity of 7%; in both Districts 2 and 4 there was a downturn of 9%. Average depth figures continued to increase; in Districts 1, 2, and 4, wells were drilled an average of 31%, 7%, and 4% deeper, respectively. The success rate of District 1 improved from 37% to 51%, whereas District 2 fell from 66% to 48% and District 4 remained the same at 60%.

There were 27 new onshore Miocene reservoirs found; however, there were no new fields discovered.

There were 272 Oligocene discoveries made onshore in 1981. In the Frio trend, successful exploratory activity was down 27% with 204 new reservoirs found. Vicksburg trend activity levels remained steady with 68 new discoveries made.

Eocene discoveries totaled 168, down 23% from 1980 totals. The Wilcox Group, the dominant Eocene producing trend, was successfully explored for 109 new reservoirs.

Activity in the Cretaceous trend was up 56% in 1981 with 148 discoveries made. The most concentrated drilling was in the Austin Chalk-Buda producing areas of Frio, Gonzales, and Wilson Counties.

There were 2 Jurassic discoveries, 1 in McMullen County and the other in Bastrop County.

Exploration activity in the south Texas offshore area resulted in the finding of 13 new reservoirs, 5 of which were new fields.