A mathematical model utilizing ideal adsorbed solution theory (IAST) and micropore size distribution (MPSD) concept to describe the adsorption equilibrium and surface energetic heterogeneity is used to predict the desorption and displacement kinetics of mixed gases in activated carbon. The model takes into account the intraparticle diffusion in both pore volume and adsorbed phase. The driving force for surface diffusion is the chemical potential gradient, and the apparent surface diffusivity is a function of the adsorbed concentration. The adsorbate-adsorbent interaction energy is related to the micropore size by the Lennard-Jones potential, and the matching energies between different species in the adsorbed phase are therefore described by this adsorbate-pore interaction mechanism in both equilibrium and diffusion of the adsorbed species. The overall adsorption isotherm and the diffusion flux of the adsorbed species are the integrals of their corresponding local values over all MPSD range accessible by the adsorbate molecules. The size exclusion effect is taken into account in the competition of the different gases for the given pore. The model parameters are obtained using only information of pure gas equilibrium and mass transfer. The model predictions are tested with the desorption and displacement kinetics data of binary gases on Ajax activated carbon and found to be in good agreement with the experimental data. (C) 2002 Elsevier Science B.V. All rights reserved.