AbstractThe influence of the macrostructures of LSCF hollow fiber membranes on oxygen permeation flux was investigated experimentally and theoretically. According to the results, asymmetric membranes perform differently toward oxygen permeation depending on their sintering outcome. If both, outer and inner surfaces of the asymmetric membrane are fully densified, finger‐like pores become dead volume, which has adverse effects, and the oxygen permeation flux is similar to that of the symmetric membrane. This implies that the improved bulk diffusion due to the reduced membrane thickness is compromised by the additional exchange reaction resistance from the enclosed macrovoids in the asymmetric membranes. However, when one surface of the membrane is fully open, then oxygen permeation is greatly enhanced mainly due to the remarkable increase in the effective surface area for surface exchange reactions. In order to evaluate the actual surface exchange area due to the presence of the porous structure within the asymmetric membranes, a correction factor α, has been introduced in the theoretical analysis presented. © 2010 American Institute of Chemical Engineers AIChE J, 2010