Abstract: An automotive power steering system having a gas pressurized oil reservoir. A gas chamber is defined within the oil reservoir above the surface level of the oil therein. The surface level and volume of the gas chamber vary as the temperature of the oil changes. A cap on a fill port of the reservoir above the maximum oil level seals the gas chamber. A fill valve and a gas accumulator are connected to the gas chamber. The gas chamber is charged to a predetermined pressure above atmospheric pressure. As the oil heats up and the oil level in the reservoir rises, the volume of the gas chamber decreases. Gas is forced from the gas chamber to an expansible chamber of the accumulator to minimize the pressure increase in the gas chamber.