A gas system has a first compressor stage for compressing a process gas. The first compressor stage includes an intake side and a pressure side. A seal gas is provided outside the first compressor stage in order to prevent process gas from issuing from leaks in the first compressor stage, having at least one second line for returning a gas mixture issuing from the gas system, this mixture including at least of process gas and seal gas. The at least one second line is configured for returning the issuing gas mixture to the intake side of the first compressor stage and/or to a location in the gas system upstream of the first compressor stage.