The invention relates to an inerting system as well as an inerting method for reducing oxygen in which an oxygen content which is predefinable and reduced in comparison to normal ambient air is set and maintained in the spatial atmosphere of an enclosed room (2). To this end, the inerting system (1) comprises a compressor system (3) for compressing an initial gas mixture as well as a gas separation system (10) connected to the compressor system (3). At least a portion of the oxygen contained within the compressed initial gas mixture is separated in the gas separation system (10). The gas separation system (10) is designed to be selectively operated in either a VPSA mode or a PSA mode.