The performance of an internally multi-staged membrane permeator in oxygen enrichment from air has been studied experimentally and compared with predicted values based on theoretical considerations. The observed experimental results give fairly good agreement with theoretical predictions and also indicate that the increase in oxygen enrichment in the internally multi-staged permeator is most pronounced when the stage number was increased to 2 or 3 at low overall stage cuts. Simulation results show that the optimal performance of the permeator can be obtained by properly selecting the stage cut parameter, E(phi), and stage pressure parameter, E(r), which are functions of individual stage cut and intermediate pressure, respectively. A comparative study between the internally multi-staged permeator and a conventional single-stage permeator indicates that, under the same energy consumption, the former offers higher degree of separation, but requires much larger membrane area.