A study of various transmissions for advanced automotive single-shaft gas turbine and turbo-Rankine engines led to selection of a variable ratio hydromechanical transmission as the most promising transmission on a near-term development basis. Detailed design analysis of this transmission showed that, in comparison with a 3-speed automatic transmission, it had approximately the same weight, was 28% smaller in size, and initial production cost could be 30-40% greater. The comparable weight of the selected transmission suggests that, with future production development, the cost could approach that of the 3-speed automatic. From a performance viewpoint, the selected transmission offered significant fuel economy advantages for a single-shaft gas turbine. For the turbo-Rankine engine, the selected hydromechanical transmission offered little performance advantage compared to a conventional automatic transmission, unless future design developments for this type of engine result in increased sensitivity of specific fuel consumption to engine speed.