The Bayou Carlin-Lake Sand area is part of a well-known "hot belt" and geopressured region of south Louisiana. The area is characterized by a rim syncline (with Cote Blanche salt dome) on the northwest, a gulfward-dipping growth fault on the south, and productive structures of Lake Sand, East Lake Sand, and Bayou Carlin fields. Lake Sand field produces mostly gas from the anticline on the downthrown side of a growth fault. In East Lake Sand field gas accumulations are on the upthrown side of the eastward extension of the growth fault. Bayou Carlin field consists essentially of stratigraphic traps north and northeast of the two fields. The mapping of the geopressured zone shows that its roof shallows over the structural highs and the downthrown side of the growth fault, an that the geopressure roof has thermal halos over the structural highs. The geothermal mapping of structural horizons in the hydropressured and geopressured zones indicates that the isothermal contours approximate the subsurface structures. The geoisotherms (depth contours) of the 250°F (121°C) datum and isotherms (temperature contours) at four depth levels (10,000; 12,000; 14,000; and 16,000 ft or 3,048; 3,658; 4,267; 4,877 m) suggest that the structural highs are associated with thermal highs, and that the rim synclinal zone of the Cote Blanche salt dome is hot because of a greater heat flow from the salt diapir. These features also are reflected by the computerized residuals of the isotherms from the first-order polynomial surfaces at those depth levels. The geothermal highs on the productive structures, particularly those associated with growth faults, easily are explainable in terms of the mechanism of primary migration of hot fluids from the deeper levels up the fault planes into the permeable sand bodies in the vicinity of the faults. The geothermal mapping technique, possibly with appropriate computer applications, has great potential as an effective adjunct to the conventional tools used for petroleum exploration. The geothermal approach is recommended for selecting areas of possible petroleum prospects prior to detailed appraisal, for delineating untested rollover anticlines against growth faults, and for locating deeper hydrocarbon accumulations of commercial significance.