The adsorption energy heterogeneity was studied by simulation using the Grand Canonical Monte Carlo method and the slit pore geometry. Nitrogen adsorption was simulated at 77 K in pore sizes ranging from 0.46 to 2.06 nm. The microscopic description of the adsorption phenomena is shown in terms of the density profile and the energy distribution function. Relation between the shape of the isotherm curve and the corresponding density profile has been discussed according to an odd or even number of layers inside the pore. Pore size distribution (PSD) for a commercial-activated carbon was calculated comparing experimental and simulated adsorption isotherm data. The energy distribution function was obtained for the pore size range above mentioned and was compared with the corresponding adsorption potential distribution. PSD obtained from experimental isotherm is combined with the energy distribution functions to propose a total energy distribution function for this material. (c) 2005 Elsevier B.V. All rights reserved.