This paper reports a thermodynamic analysis of filling a fuel tank with compressed gaseous hydrogen. The analysis is based on energy and exergy methods. A parametric study is performed to investigate the effect of initial conditions on the exergy destruction and exergy efficiency of filling processes. The transient filling process is studied to determine the temperature and pressure changes inside the storage tank during filling. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.