The role of adsorption in the single and binary permeation of CH4 and CO2 through a silicalite-1 membrane has been investigated. Adsorption on the zeolite is favorable for CO2, resulting in selectivity for CO2 in the permeation. The generalized Maxwell-Stefan (GMS) equations, in combination with the ideal adsorbed solution theory (IAST), were used to model their binary permeation. It is found that the use of accurate adsorption data is of utmost importance for extracting transport properties from the single-component permeation as well as for modeling multicomponent permeation. The GMS model qualitatively and quantitatively predicts the temperature-dependent properties of the mixture permeation, while it slightly deviates from the experimental observation on the pressure dependence of the mixture selectivity. This deviation is ascribed to intercrystalline or surface barriers for the larger molecule CH4 in the membrane as well as to the overprediction of the CO2 loading in the zeolite by the IAST.