The work involved in identifying geothermal fields can be simplified by means of a Geographical Infomation System (GIS), a decision-making tool used to determine the spatial association between exploration and environmental thematic maps. This methodology has been applied to part of the Sabalan geothermal field in northwestern Iran, and to the siting of exploration wells. The datasets used in the analyses consist of geological, geochemical and geophysical information. Boolean and Index Overlay knowledge-driven models were developed for site selection; the findings from these two models correlated well with the exploration data modeling. The results of the Index Overlay model were combined with those of an environmental suitability analysis for final selection of well Sites. The results of exploration and environmental data modeling were combined to select and prioritize the sites of three exploratory wells in the study area. (c) 2007 Elsevier Ltd. All rights reserved.