Abstract: A propulsion system for a vehicle comprising a hydrostatic transmission wherein the system typically includes an electric motor, a hydrostatic pump preferably of the continuous variable displacement type, hydrostatic motors for cooperation with the wheel axles of the vehicle, and a gas accumulator which provides for the compression and expansion of a gaseous medium depending on whether the transmission fluid is being pumped into or withdrawn from the gas accumulator. The gas accumulator comprises a pressure vessel which serves as a structural member of the vehicle. It may have a tubular configuration disposed as a load-bearing structural member of the chassis or it may comprise a number of interconnected pressure-retaining panels, that form the vertical sides and/or roof sections of the vehicle. Suitable mechanical and electrical/electronic controls are provided to monitor the gas pressure in the gas accumulator and to regulate the stroke and function of the hydrostatic pumps and motors.