Molecular dynamics simulations are performed for the physisorption of molecular Hydrogen in single walled carbon nanotubes (SWNTs). The distribution of the adsorbed H-2 Molecules in nanotube bundles of different size is analysed in detail. An interpretation of the observed distributions is given in terms of a simulated potential energy surface which considers all present pair interactions for a single hydrogen molecule. The effect of the nanotube diameter in the H-2 adsorption capacity of SWNT bundles is also commented. (C) 2007 Elsevier B.V. All rights reserved.