Advanced energy conversion technologies are being investigated by the Power Technology Division (PTD) of the NASA Lewis Research Center. Among the technologies are batteries, induction motors, high frequency electric power management and distribution, dynamic energy storage, and Stirling cycle machines. While the emphasis of the Division is the application of these technologies to fulfill space power requirements, many terrestrial applications exist.This paper presents a study assessing the feasibility of a hybrid electric vehicle based on some advanced technologies being investigated by the PTD. The study considers fuel economy, emissions, driveability, performance, and range of a mid-size, current production vehicle (Taurus) operating in the hybrid mode. A vehicle with a 20.1 kWe (27 hp) free-piston Stirling power convertor as the prime mover, and a flywheel as the energy storage device was modeled. Based on emission data from a Stirling powered vehicle, emissions are projected for the hybrid vehicle operating with gasoline and compressed natural gas as the fuel. The projections indicate that a Stirling powered hybrid electric vehicle based on current technology can comply with the California Ultra-Low Emission Vehicle regulations.