Highly efficient energy conversion systems with fuel cells for vehicles and stationary applications are currently being discussed all over the world as a technology which will be able to reduce primary energy demand and emissions of limited and climate-relevant pollutants. The high flexibility of fuel-cell systems with respect to energy carriers opens up possibilities of modifying the energy market in the long term. New environmental legislation, above all in the USA, stipulating the introduction of emission-free cars from 2003, has led in the transport sector to an intensified search for alternatives to conventional drive concepts. In stationary applications, numerous demonstration plants and some field tests already implemented reflect the developmental stage of fuel-cell systems. In Germany, a new combined heat and power (CHP) plant modernisation law has been enacted. This act is of special significance for the market launch of fuel cells. A major milestone on the road to market success for all the above-mentioned systems-in order to compete with conventional technologies-is the reduction of costs. In this contribution systems analyses for mobile and stationary applications of fuel-cell systems are presented as well as economic analyses for different fuel-cell systems for stationary applications. In particular, CHP generation based on natural gas as the energy carrier is performed. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.