The Monte Carlo method in its grand ensemble variant (GCMC) it; used in combination with experimental data in order to characterize microporous carbons and obtain the optimal pore size distribution (PSD). In particular, the method is applied in the case of AX-21 carbon. Adsorption isotherms of CO2 (253 and 298 K) and H, (77 K) up to 20 bar have been measured, while the computed isotherms resulted from the GCMC simulations for several pore widths up to 3.0 nm. For the case of H-2 at 77 K quantum corrections were introduced with the application of the Feynman-Hibbs (FH) effective potential. The adsorption isotherms were used either individually or in a combined manner in order to deduce PSDs and their reliability was examined by the ability to predict the experimental adsorption isotherms. The combined approach was found to be capable of reproducing more accurately all the available experimental isotherms. (c) 2007 Elsevier B.V. All rights reserved.