A site energy distribution function is proposed that can rapidly generate the binding energy distribution of any adsorbent for any target molecules using only the Sips isotherm parameters, the advantages of which are discussed. The proposed model is successfully applied to determine the site energy distribution of a series of activated carbons, activated carbon fiber, and single-wall carbon nanotubes (SWCNT) for the adsorption of several gas molecules. The proposed model revealed the fact that the sorption capacity of the activated carbons for the target molecule depends on the shape and the size of the binding site energies. The proposed model is very simple to use and does not need any complicated or sophisticated computer programs to determine the distribution of binding energies on the adsorbent surface.