Two engine technologies (Brayton cycle and Stirling cycle) currently being pursued by the US Department of Energy were examined for their potential impacts if they achieved commercial viability. An economic analysis of the expected response of buyers to the attributes of the alternative engines was performed. Hedonic coefficients for vehicle fuel efficiency, performance and size were estimated for domestic cars based upon historical data. The marketplace value of the fuel efficiency enhancement provided by Brayton or Stirling engines was estimated. The effect upon various economic sectors of a large scale change-over from conventional to alternate engines was estimated using an economic input-output analysis. Primary effects were found in fuels refining, non-ferroalloy ores and ferroalloy smelting. Secondary effects were found in mining, transport, and capital financing. Under the assumption of 10 years for plant conversions and 1990 and 1995 as the introduction date for turine and Stirling engines respectively, the comparative fuel savings and present value of the future savings in fuel costs were estimated.