A common computational method for the characterization of porous materials is to calculate the adsorption isotherm of fluids in the materials from the preassumed wall-fluid potential. If the wall-fluid potential is unknown, the common computational method becomes invalid. In a realistic experiment, however, it is common to know the experimental adsorption isotherm of nitrogen and not to know the wall-fluid potential. Here we propose a stepwise approximation for modeling wall-fluid potential under conditions where only the adsorption isotherm of nitrogen is measured experimentally. Based on the modeled wall-fluid potential, we can characterize the porous materials and predict the adsorption of other adsorbates on the materials. It is expected that the approach would provide a powerful means for the characterization of novel materials under conditions where only the experimental adsorption isotherm is available. (c) 2006 Elsevier Inc. All rights reserved.