For medium and long range considerations of twenty to fifty years, i.e. up to the years 2000 and 2030, the growth of energy demand should be considered in a global context. Interdependence will grow. In the study `Energy in a Finite World' of the International Institute for Applied Systems Analysis (IIASA), Austria, demand and supply scenarios were elaborated in detail for seven world regions. One of the striking features of these scenarios is the strong and significantly increasing demand for liquid or gaseous hydrocarbons despite energy conservation and substitution measures. On the supply side this means more and more unconventional fossil fuels such as shale oil, tar sands and low-grade brown coal. In this paper we consider a transition from the current energy systems to novel fossil energy conversion and distribution systems that will contain all of the mass streams and thereby avoid environmentally hazardous emissions. It is then natural to extend these considerations to prospects for a sustainable hydrogen-based energy system in the far future which would not be constrained by resource limitations.