Methane transport was evaluated using column tests for simulated interim cover profiles composed of soil only or soil over a geomembrane (GM). Tests were conducted with a co-extruded GM of ethylene-vinyl alcohol (EVOH), a linear low-density polyethylene (LLDPE) GM, a polyvinyl chloride (PVC) GM, or a polyethylene (PE) geofilm used in conjunction with one of three soils (clay, silt, or sand). Methane breakthrough from the simulated covers with LLDPE and PVC GMs (6–8 days) was approximately three times more rapid relative to the cover with the EVOH GM (22 days). Breakthrough from the simulated cover with a geofilm (2 days) was ten times more rapid relative to the cover with the EVOH GM. Methane diffusion coefficients for the co-extruded EVOH GM obtained by inversion of the column data were 19–29 times lower than diffusion coefficients for the conventional GMs and the .1-mm PE geofilm. Soil type had minimal influence on methane transport through the interim covers relative to GM type. Predictions made with a numerical model parameterized using diffusion coefficients obtained from the column tests indicate that methane fluxes from interim landfill covers with an EVOH GM are approximately two orders of magnitude lower than methane fluxes from an interim cover with a conventional GM and six orders magnitude of lower than with soil alone.