Abstract: A parallel hybrid drive system for self propelled vehicles including a direct current motor-generator having a drive shaft in common with an internal combustion engine leading to a variable speed transmission and a final drive train. The motor-generator has a no-load speed, established by a separate field exciter, below which it drives the shaft as a motor and above which it is driven by the shaft as a generator. Storage batteries are operatively connected to the motor-generator to supply power to it below the no-load speed. The internal combustion engine operates over a small RPM range around its most efficient speed at a power level established by a fixed throttle setting. The transmission is operatively connected to an accelerator and direction selector switch to vary the speed and direction of the vehicle.