A direct comparison of experimental measurements (coherent quasielastic neutron scattering) and simulation (molecular dynamics) is carried out for the first time to investigate the concentration dependence of transport diffusivity of nitrogen and carbon dioxide in silicalite-1. Theoretical elaboration of the simulation results on the basis of the quasichemical mean field approximation and a model of surface diffusion due to D. A. Reed and G. Ehrlich (Surf. Sci. 1981, 102, 588) leads to the conclusion that the corrected (Darken) diffusivity Do can exhibit significant dependence on the loading theta of the sorbed phase, varying with the strength of interactions between the sorbate molecules. As a consequence of sorbate-sorbate interactions being considerably more attractive in CO2/silicalite-1 than in N-2/silicalite-1, D-0(theta) is a decreasing function in CO2/silicalite-1 but displays a weak maximum in N-2/silicalite-1.