Abstract: A single stage secondary oxygen concentrator for receiving a gas mixture from a first stage oxygen concentrator and a method of use therefor is disclosed. The concentrator includes a first carbon molecular sieve bed and a second carbon molecular sieve bed. A first inlet valve is connected to an inlet of the first carbon molecular sieve bed and a second inlet valve is connected to the inlet of the second carbon molecular sieve bed. A first product outlet valve is connected to the outlet of the first carbon molecular sieve bed and a second product outlet valve is connected to the product outlet of the carbon molecular sieve bed. The oxygen concentrator has control means for controlling a first cycle in which the first carbon molecular sieve bed is being charged with the gas mixture and the second carbon molecular sieve bed is being desorbed.