Forward modeling of coupled fluid and heat flow in the Powder River basin, Wyoming, is used to explain anomalously high heat flow values observed in the southern portion of the basin. Effective basin-scale permeabilities of selected Powder River basin aquifers and aquitards were calibrated by matching surface heat flow measurements to simulation results. Fractures associated with a large anticline in the southwestern part of the basin were found to play a major role in the basin's thermal regime. While the model results are non-unique, they demonstrate that regional structural features play an important role in a basin's overall energy budget and fluid flow regime. With the results of the basin-scale model it is possible to evaluate regional-scale flow and transport processes. ¿ 2001 American Geophysical Union