The invention relates to an inerting method as well as an inerting system (1) to set and/or maintain a reduced oxygen content in an enclosed room (2), wherein a gas separation system (3.1, 4.1; 3.2, 4.2; 3.3, 4.3) is provided which separates off at least a portion of the oxygen from an initial gas mixture provided in a mixing chamber (6) and by so doing, provides a nitrogen-enriched gas mixture. In order to optimize the operation of the inerting system (1), the invention provides for a portion of the air to be withdrawn from the enclosed room (2) and admixed with fresh air in the mixing chamber (6).