Dry, oil free air at ambient temperature and elevated pressure is passed through vessels (adsorbers) containing molecular sieve. The sieve holds on to (adsorbs) Oxygen molecules in preference to the nitrogen molecules, thus separating nitrogen from air. The oxygen molecules are released (desorbed) from the sieve when the pressure in the adsorber is reduced, thus making the sieve fresh again (regeneration). Two vessels are employed for continuous supply of nitrogen. The entire cycle is microprocessor controlled and no operator attention is required for normal operation.