The literature demonstrates the detrimental effects of variability in the inner diameter, permeance, and selectivity of hollow fiber membranes for the production of a retentate product, for example, nitrogen purification from air. This past work is extended to the production of a permeate product. Additionally, simultaneous variation of multiple fiber properties is considered. Fiber variability is detrimental to permeate production; the ratio of product to feed flow rate decreases with an increase in variability. However, the permeate product flow rate remains unchanged in contrast to the large changes observed for a retentate product. Simultaneous, independent variation of multiple fiber properties makes performance worse. However, correlations between the variations in fiber properties can improve performance. Theoretical performance predictions compare favorably with experimental measurements for the production of oxygen from air if either simultaneous variation of fiber size with permeance occurs or significant deviations from countercurrent flow exist. The results may be used to develop manufacturing guidelines for the production of hollow fiber membranes.