The large sedimentary basins of Texas have been and are currently the subject of intensive petroleum exploration and production. The Gulf Coast, East Texas, the Anadarko Basin, and West Texas have all produced significant volumes of both oil and gas. Many of the fields and reservoirs within these basins are now mature or reaching the end of their productive lives and present an opportunity for these deep formations to be transitioned from petroleum production to geothermal-energy production using the existing infrastructure and the legacy of geologic information created by the oil and gas industry. The Gulf Coast and the Anadarko Basin have previously been analyzed for thermal energy in place, although formations in East and West Texas have not. A problem lies in the fact that previous studies may have overestimated thermal energy by employing a more simplistic method, in which a basin is split into one or more uniform-temperature blocks for which thermal energy in place is calculated. This is overcome in the present study by using ArcGIS to create a maximum extractable depth raster for both maximum well depth and maximum extractable depth in regions of Texas. The thermal energy in place is then derived through integration of the geothermal gradient raster over the block volume defined by the maximum depth raster to estimate thermal energy in place. A reference temperature of 93 C (200 F) is used. The results of this methodology indicate that 1.66E + 23 Joules (2.71E + 13 bbl oil equivalent) reside in place in Texas that is accessible using existing wells. Regionally the Gulf Coast contains 3.20E+ 22 Joules (5.24E+ 12 bbl oil equivalent), East Texas contains 4.04E+ 22 Joules (6.60E+ 12 bbl oil equivalent), West Texas contains 1.42E + 22 Joules (2.32E + 12 bbl oil equivalent), and North Texas contains 4.20E+ 21 Joules (6.87E+11 bbl oil equivalent). (C) 2013 Elsevier Ltd. All rights reserved.