Approximate solutions for gas separation by hollow fiber membranes have been developed by several investigators. However, there are few reports of experimental verification of the models for high stage cut separations. In this work, an approximate mathematical model was developed and was experimentally verified for high stage cut air separation. Both countercurrent and cocurrent now patterns were used. In addition, the applicability of feed-inside mode for low stage cut air separation by hollow fiber membrane was examined. It was found that feed-inside mods was more advantageous than feed-outside mode when used for the generation of oxygen-enriched air.