Existing detailed models of gas permeation through zeolite membranes have focused oil adsorption and diffusion within zeolite crystals. Practical zeolite membranes, however, are typically grown as thin films on porous supports and are often studied experimentally in the presence of a sweep gas in addition to the permeating species of interest. We have used a combination of atomically detailed and continuum models to examine the impact of sweep gases and porous supports on permeation of CH4 through silicalite membranes at room temperature. The adsorption and transport properties of the gas mixture inside the zeolite are treated using atomically detailed models, whereas transport in the porous support is treated using well-validated continuum models. Our results indicate that the effect of He as a sweep gas on unsupported membranes is minor. In many cases, the use of a porous support when no sweep gas is present also has only negligible effects compared to that of an unsupported membrane. When a sweep gas and a porous support are present, however, strong deviations from the permeation properties of an equivalent unsupported membrane with no sweep gas can occur, and these effects can depend strongly on whether the support faces the feed or permeate side of the process. These observations are related to existing experimental studies of gas permeation through zeolite membranes. (C) 2005 American Institute of Chemical Engineers.