New concepts are introduced in this paper to account for the enhancement of the potential energy of interaction between adsorbate molecules and surface atoms within the pore interior. With these concepts, a structure based model is developed to describe the adsorption equilibria in heterogeneous activated carbon. The model. requires only molecular properties of the adsorbate and adsorbent, and the structural heterogeneity is accounted for with the distribution of micropore size. This model is validated with the adsorption data of nitrogen and methane on carbonaceous materials under supercritical conditions. It is found that the model is capable of describing very well the adsorption of supercritical gases in porous media and could be used as a tool to analyze the micropore size distribution.