An instance of regional variation in Oklahoma and two cases of local variation, one at Long Beach, California, and the other at Salt Creek, Wyoming, have been selected for consideration from a large number of geothermal surveys conducted during the past few years by the U. S. Geological Survey and the American Petroleum Institute. The causes of local and regional variations are unknown. Possible explanations such as radioactivity, proximity to crystalline rocks, and transfer of heat along the strata are given careful consideration in attempting to explain the observed relations between the strata and the isogeothermal surfaces.