The hypothesis accepted herein is that heat flows from the Earth's hot interior toward its colder surface is nature's attempt to establish temperature equilibrium. The following three facts are accepted. 1. Hydrocarbon fluids have very low thermal conductivities. 2. Equal heat input elevates the temperature of a largely hydrocarbon fluid volume relative to a laterally equivalent volume of largely water-filled porosity. 3. There are fewer grams of hydrocarbon fluids to warm than there are grams of water filling an essentially equal porosity volume. The technique formulated involves the following steps: (1) calculation of geothermal gradient values, (2) creation of a geothermal gradient field areally, (3) vector analysis or contouring of created data, and (4) anomaly definition. Results for three examples (Black Lake Field, Louisiana; Haverhill Field, Kansas; and Salt Creek Field, Texas).--Modified journal abstract.