Over-all drilling activity in South Texas increased 10 per cent over 1963. Wildcat completions rose 12.5 per cent and had a success ratio of 1:5. Development drilling increased 9 per cent and was 71.2 per cent successful. Production of oil increased 4.1 per cent over 1963, and gas and gas liquids production also showed gains. Industry interest was focused on deep drilling ventures along the Jurassic Smackover Limestone and down-dip Yegua trends. Another center of attention was in Wilson, Gonzales, and Gaudalupe Counties where the discovery of four shallow Poth Sand (Paleocene-Eocene) fields led to large-scale development programs. The Oligocene-Miocene trend continued as South Texas' most active area with 47 per cent more exploratory drilling than in 1963. Deeper drilling highlighted the exploration program, as it did in the other trends. Geophysical activity decreased 24 per cent from 1963; the most severe reduction was in the Lower Eocene trend. Experimental programs were widespread and introduced several new deep investigation techniques.