Using the Maxwell-Stefan approach, expressions have been derived for the diffusion of mixtures of hydrocarbons in zeolites wherein the individual components have different saturation loadings. This Maxwell-Stefan diffusion model, in combination with the Ideal Adsorbed Solution (IAS) theory and the single-component adsorption isotherms, provides a superior, qualitative and quantitative, prediction of the permeation fluxes of ethane/methane and propane/methane mixtures through a silicalite-1 membrane. The difference in adsorption saturation loadings becomes apparent in the entropy effects in the mixture adsorption.