This study reports an analysis of membrane permeance and mass transfer coefficient in laboratory test cells for gas separation using computational fluid dynamics. Mass transfer coefficients and species concentration were computed across the membrane surface for gas mixture. The same test cells were examined for the fluid hydrodynamics in liquid separation. It was observed that the uniform flow distribution in the case of gas separation was responsible for improved permeance; whereas, a uniform flow had no significant effect on permeation rate for liquid separation. Also, the potential reasons for the difference in gas and liquid separation are discussed. (C) 2009 Published by Elsevier B.V.