A survey conducted by the Swiss Federal Office of Energy in the mid 1990s proved that a significant number of existing tunnels, with an estimated total heat potential of 30 MWt, is suitable for further development. The tunnel water available in five sites in the Alps is currently utilised for space heating and sanitary warm water supply, and five more will be available in the near future. An additional 30 MWt of geothermal energy is estimated to be available at the portals of two important Alpine tunnels now under construction, the Lotschberg (35 km long) and the Gotthard (57 km). A further approximately 35 MWt is expected from tunnels scheduled for construction during the next ten years. A total of almost 80 MWt could thus be achieved by 2012-2014. Theoretical estimates of the geothermal potential of future tunnels also account for cooling effects and the inevitable reductions in water inflow rate during and after tunnel construction. Advanced computational methods and practical tools for potential assessment have been developed in order to obtain realistic values and thus facilitate the early planning of near-portal heating systems. Careful planning and close cooperation between tunnel management and heat consumers can contribute to optimizing the utilization of this interesting form of geothermal energy. (C) 2003 CNR. Published by Elsevier Ltd. All rights reserved.