The Maxwell-Stefan formulation of diffusion in multicomponent mixtures is used to obtain explicit formulae for calculating the diffusivities of binary mixtures within a zeolite matrix. The theoretical development allows the estimation of the mixture diffusivities on the basis of the purl component diffusivities at zero loadings. The applicability of the Maxwell-Stefan model is demonstrated by comparison with published molecular dynamics simulations for mixtures of methane-perfluoromethane, methane-xenon, and methane-n-butane in silicalite.