The intensive 20th-century search for fossil fuels has been driven by a growth in global energy demand that was exponential until the oil crises of 1973 and 1979 (Fig. 12.1a). Consumption continues to increase, by over 50% in the two decades to 1990. This chapter assesses the potential of fossil fuel reserves to supply future energy demands. It then reviews alternative energy sources, particularly those involving geological factors, and their abundance in the British Isles.