A hybrid air separation process for oxygen production uses a membrane gas permeator with bypass to increase the oxygen concentration of the feed to 23.5% before the cryogenic distillation plant. A 23.5% limit on oxygen is required to avoid use of more expensive construction materials. By pre-concentrating the oxygen, the feed flowrate to the compressor, heat exchangers and the distillation column can be reduced by 11%, which reduces power requirements and sizes of the downstream equipment. Achieving this concentration with very low energy requirements is surprisingly difficult with commercially available membranes. New membrane materials with higher fluxes and selectivities could make the process more economical.