Both detailed and regional 3D geological models have recently been increasingly used for application to natural resource assessment and management. In addition to their principal use in petroleum exploration, significant advances in multidimensional geological mapping have occurred in the field of mineral resource and groundwater exploration. These applications have required incorporation of large databases of geological, geophysical and hydrogeological data into 3D geological models. Methods developed for subsurface analysis of oil and groundwater resources are now being extended for application to geothermal resource assessment. The distribution of reservoir and petrophysical rock properties, as well as thermal regime of rock units, are a significant factor for assessment of geothermal reservoirs as a potential source of renewable energy. Regular grid solids created in a 3D model can be converted into a tetrahedral mesh for finite element modeling of reservoir properties as well as complex mass and heat flow analyses. Thus, application of 3D geological modeling in hydrogeology of geothermal waters is becoming increasingly important in natural resource assessment.