A PSA method incorporating the invention is applicable to the separation of a preferred gas from a mixture of the preferred gas and a less preferred gas. The PSA method uses an adsorbent bed including one or more layers of O.sub.2 equilibrium selective adsorbents, and comprises the steps of: pressurizing the adsorbent bed to a high pressure with a feed of air to enable the adsorbent bed to adsorb O.sub.2 ; extracting from the bed at bed pressure, a flow of N.sub.2 and storing at least some of the flow in a product tank; desorbing O.sub.2 from the adsorbent bed by feeding void gas in the bed enclosure to a storage tank and venting the adsorbent bed to a low pressure region; purging the adsorbent bed by feeding thereto the void gas from the storage tank; and repressurizing the adsorbent bed to an intermediate pressure with a flow of void gas from the storage tank.