A process for removing oxygen from a feed stream to obtain an oxygen-depleted product stream by applying the feed stream to at least one separator including a feed zone and a permeate zone separated by a solid electrolyte mixed conductor membrane, and driving a first portion of entrained oxygen in the feed stream from the feed zone to the permeate zone via the mixed conductor membrane by applying at least one of a purge stream and a negative pressure to the permeate zone to establish a lower partial pressure of oxygen in that zone. Oxygen-depleted retentate is withdrawn as a product stream. Preferably, at least one additional solid electrolyte ionic or mixed conductor membrane is also employed in feed series with the mixed conductor membrane.