Many subsurface temperature observations from South Louisiana were obtained from the Federal Power Commission. Most of the measurements were made with calibrated maximum thermometers long after the wells had been completed. Temperature-depth curves could be obtained for 123 fields. The temperature gradients ranged from 18 to 36 degrees C/km of depth; most were between 22 and 24 degrees C/km. At a depth of 3,048 m (10,000 feet) there is a belt of high temperature near the present coastline. This hot belt is located approximately where the sedimentary strata are believed to be of maximum thickness, which is estimated to be about 15,000 m. It is suggested that metamorphicm and recrystallization already have begun in the lowest part of the sedimentary section, and the consequent increased thermal conductivity may account for the high temperatures along the belt of maximum thickness.