Hybrid membrane-sorption systems for producing oxygen-enriched air have been considered in terms of the general theory of multimodular separation systems with recirculation lines. The performance of the hybrid systems has been examined as a function of the product stream pressure. The hybrid and the membrane air separation systems have been compared. It has been shown that an optimal scheme is the membrane-sorption system in which a recycle is formed by returning the retentate stream from the membrane module to the feed stream using an ejector, with the feed gas mixture being sent to adsorbers from the ejector outlet.