This work involves the investigation of the sensitivity of computational fluid dynamics based models of auto ignition of hydrogen gas escaping into the surroundings to the use of an ideal gas and a real gas Noble-Abel equation of state. Ensuring consistent modeling techniques when the real gas equation of state is implemented, real gas based thermodynamic properties, real gas based property mixture models, and real gas based chemical equilibrium constant formulations are utilized. Within the standard computational fluid dynamics models, a customized chemical kinetic equation integrator is employed. An LES based turbulence model is implemented. For tank pressures of 40, 80, and 120 MPa, differences in the gas conditions, including gas pressures, temperatures, velocities, flow rates, energy, and chemical species mass fractions, are compared. The relationships between the local and time varying gas conditions, chemical reaction indicators, the tank pressure, and the equation of state captured in the simulations are described in detail. The results clearly show the increasing deviation between the ideal gas and Noble-Abel based results as the tank pressure increases, indicating the importance of the use of the proper material model and chemical equilibrium formulation for the conditions of interest. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.