The South Texas report includes 58 counties in Texas Railroad Commission Districts 1, 2, and 4, and the offshore area. District 1 exploration activity increased 32% from 1976, with significant discoveries from the Cretaceous in Dimmit, Maverick, and Milam Counties. Although the total exploration effort was significantly greater, the success rate decreased 21%, mainly because of a drop in successful oil completions. Development activity in District 1 increased slightly with a continued 87% success rate.

District 2 exploration activity remained consistent with 1976 figures. Oil completions increased by 60% with a total exploration effort of 338 wells. The overall exploratory success rate decreased from 42% in 1976 to 39% in 1977. The heaviest sustained activity continues to be in the Frio trend of Jackson, Victoria, Refugio, and Calhoun Counties. Development activity remained constant in 1977 with 488 total wells and a 70% success rate.

District 4 exploration activity was up 33.5% from 1976, with significant discoveries in the Frio trend in Aransas and San Patricio Counties, and in upper and lower Wilcox sandstones in Webb and Zapata Counties. Oil discoveries were up significantly in 1977 with 33 successful exploration-class oil completions, including 6 new-field wells. District 4 development activity was up 29.3% in 1977 with 903 wells drilled and a total footage of 5,349,831. This increase is due mainly to activity in southern Webb County in the lower Wilcox south Laredo gas trend and in the Navarro Escondido and Olmos sandstone trend of northwestern Webb County. Exxon led in development activity, primarily with Frio-Vicksburg plays on King Ranch acreage.

The South Texas offshore area had a 22.4% increase in activity, with a total of 71 wells drilled in 1977. Significant discoveries were drilled in the Matagorda and Mustang Island areas by Corpus Christi Oil & Gas and McMoRan. Development activity increased from 3 wells in 1976 to 12 wells in 1977 with 4 successful completions.