Hydrogen release from a high-pressure chamber is to be modeled in this paper. Two approaches are developed to investigate the real gas effects at high pressures. In the first method, an analytical model is developed to simulate time histories of stagnation properties of hydrogen inside the chamber, as well as sonic properties of hydrogen at the orifice. Corresponding thermodynamic relations, which describe specific heats, internal energy and speed of sound, are derived based on the Beattie-Bridgeman state equation. Regarding the second approach, a 3-D unstructured tetrahedral finite volume Euler solver is applied to numerically simulate the hydrogen release whereby the solver is modified to take into account the real gas effects. All the required modification for calculation of real gas Jacobian matrices, eigenvectors and Roe's average convective fluxes are described. Real gas effect is thus modeled by the game state equation. Numerical and analytical results are then compared for ideal and real gas conditions and, to conclude, an excellent agreement is reported. (c) 2004 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.