A gas ballast system for a multi-stage positive displacement pump in which a first stage includes at least one positive displacement pump stage, is equipped with an inlet valve and an outlet valve, and is connected with the following stage by an intermediate vacuum chamber, with the gas ballast system including a first conduit for supplying gas into the intermediate vacuum chamber, and a second conduit for supplying gas from the intermediate vacuum chamber into a pump chamber of the first stage or to a suction region of the first stage.