This work attempts to shed light on molecular hydrogen adsorption in carbonaceous microporous materials by exploiting molecular dynamics simulations combined with geometry optimization calculations of the solid structures. Carbon structures were considered here because of evidence suggesting that they may be efficient media for hydrogen storage. The inclusion of oxygen functional groups in these solid structures was also examined since they could affect hydrogen adsorption. Insertion of oxygen functional groups causes a decrease in hydrogen adsorption and this effect is more evident in narrow pores. Hydrogen molecules adsorb in the pores as structured layers, depending on pore slit width. The amount of hydrogen adsorbed reached 4.41 % w/w for the purely carbonaceous materials, whereas for the oxygenated materials adsorption was limited to 3.30% w/w. The estimated adsorption density inside the pores exceeded the liquid hydrogen density for both solid structures investigated. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.