Hydrogen has proven to be a non polluting energy vector. However great mass production and storage facilities at high pressure are required where one of the most promising ways is metal hydrides, particularly when their surface is modified by different methods using supercritical fluids. Therefore it is important to have thermodynamics models capable to determine these conditions and particularly at phase equilibrium. The present work aims to examine and test different thermodynamic models for certain high pressure processes. This study is also an opportunity to show the importance of the choice of the most appropriate equation of state equation in association with the most suitable mixing rule, for the given operating conditions. Finally this work can be seen as a basis for considering more deeply processes which use supercritical fluids, particularly supercritical extraction and hydrogen production in supercritical water-cooled nuclear reactor. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.