The adsorption of molecular hydrogen on a three-dimensional pillared graphene structure under various environments is studied using molecular dynamics simulations. The effects of pressure, temperature, and the geometric structure of pillared graphene are evaluated in terms of molecular trajectories, binding energy, binding force, and gravimetric hydrogen storage capacity (HSC). The simulation results show that in a pillared graphene structure, the HSC of the graphene sheets is better than that of the carbon nanotube (CNT) pillars. An insufficient gap between graphene sheets decreases the HSC because hydrogen adsorbed at the edges of a pillared graphene structure prevents hydrogen from entering the structure. A low temperature, a high pressure, and a large gap between graphene sheets maximize the HSC. The HSC is only slightly improved by increasing the CNT diameter. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.