We have directly compared detailed atomistic simulations and experimental measurements of CH4/CF4 mixture permeation through a silicalite membrane at room temperature. The predicted membrane properties are fully specified by the interatomic potentials used in the atomistic simulations, since we used these simulations to describe the full binary transport diffusion and binary adsorption. This approach does not require any assumptions about the relationship between self-diffusion and transport diffusion or about the behavior of cross-species coefficients. This is the first time that predictions from a detailed model of this kind have been compared with experimental data for mixture permeation through a zeolite membrane. The atomistic theory correctly predicts that the silicalite membrane is CF4-selective to mixed CH4/CF4 feeds while the ideal selectivity of the same membrane predicts CH4 selectivity. While some quantitative discrepancies between the predicted and experimentally observed selectivities exist, these can be related to known shortcomings of the interatomic potentials used in our atomistic simulations. (C) 2003 Elsevier B.V. All rights reserved.