Using the Maxwell-Stefan (M-S) diffusion equations as a basis, we derive simple analytic expression for the estimation of component permeances of mixtures across micro- and mesoporous membranes on the basis of unary permeation data. The analytic procedure uses two simplifying assumptions: (1) downstream pressures are negligibly small in comparison to upstream pressures, and (2) adsorption equilibrium within the pores can be described by Henry law coefficients. Two limiting scenarios are considered in estimating the M-S exchange coefficients, D(ij): (1) correlations negligible, and (2) correlations dominant. In the correlations negligible scenario, the permeances of each component in the mixture equal that of the corresponding pure components. For the correlations dominant scenario, the permeances in the mixture are significantly different from the pure component values: the differences being dictated not only by mobilities of the species within the pores, but also by the adsorption equilibrium. The results of this study underlines the strong influence of diffusional correlations on the mixture permeances and permeation selectivities. (C) 2010 Elsevier B.V. All rights reserved.