Initiated by separation factors of up to 15 between CH4 and H-2 found in experiments of gas mixture permeation through a newly developed ZIF-8 membrane the diffusion of CH4 and H-2 in ZIF-8 has been investigated by IR microscopy and molecular dynamics simulations. Several well known interaction parameter sets for simulations have been tested. It turned out that the H-2/CH4-ZIF-8 system is very sensitive with respect to the choice of these parameters. The large differences in the diffusion behavior of CH4 and H-2 are investigated by microscopic simulation tools and compared with experiments. A parameter set has been found that gives reasonable agreement with experimental IR and membrane permeation results. (C) 2011 Elsevier B.V. All rights reserved.