Synthetic fuels vary in the character and magnitude of the environmental impacts associated with their production. Oil shales - with its large volume of solid waste, heavy withdrawal of water and air pollution - will have the greatest impact. Less damage results from coal liquefaction in spite of higher water requirements, the risk of surface water pollution, and poor conversion efficiency. Coal gasification produces the least damage, but more research and caution are called for with all synthetic-fuel development. (DCK)