The Malm of the Southern German Molasse Basin, known as fissure-karst-aquifer, is regarded as a significant reservoir of geothermal energy in central Europe with respect to production of heat as well as electrical power. Existing exploration results from various projects provided reliable parameters for long-term modelling of economical aspects at regional scale for the first time. The aim of the present project is to investigate the sum total capacity of this reservoir and the width of the area of mutual influence of several adjacent geothermal plants by numerical modelling.