A site energy distribution function for carbon adsorbents is proposed for the adsorption equilibrium data following a Redlich-Peterson isotherm. The proposed model is successfully applied to determine the site energy distribution of two pitch-based activated carbons (PA and PBA) developed in our laboratory and also for other common adsorbent materials for different gas molecules. According to the proposed model the site energy distribution curve for carbons PA and PBA are found to be unimodal for N-2 gas molecules at 77 K. The proposed model successfully predicts the site energy parameters of both homogeneous and heterogeneous adsorbents. (C) 2010 Elsevier B.V. All rights reserved.