In the present work, a one-dimensional mathematical model is developed to analyze the concentration polarization phenomenon for the separation of gas mixtures in composite hollow fiber membranes. An analytical expression is developed for determining the interfacial concentration at the interface of dense and porous support layers. Further, the model accounts for the non-ideality of the gas mixture. Both co-current and counter-current flow configurations for the separation of hydrogen from a three-component mixture are studied. The effects of feed side pressure and velocity as well as permeability on concentration polarization are probed. It is apparent from this study that the concentration polarization phenomenon significantly affects the separation efficiency at higher permeability values.