Hybrid powertrain configurations were evaluated for several classes of vehicles. This paper presents a discussion of the type of hybrid powertrain configurations evaluated, their respective mode(s) of operation, a discussion of computer simulation of powertrain/vehicle performance, and the effect of the performance of several key powertrain components such as heat engine, battery, and electric drive motor on vehicle emissions.Based on power and torque requirements for various classes of vehicles as derived from basic specifications and performance guidelines, it was found that the necessary hybrid powertrain configurations would be composed of major components of a relatively feasible efficiency and size. It was also found that vehicle emissions are relatively sensitive to electric drive motor efficiency and relatively insensitive to battery recharge efficiency. Driving-cycle characteristics were shown to have a significant effect on theoretical average emission levels. Overall, the results suggest that the hybrid/electric powertrain appears to offer promise as a means of obtaining low-emission vehicles compatible with the 1975-1976 Federal Emission Standards.