A method for the prediction of the LFL at high pressures, where data are scarce, based on the calculation of adiabatic flame temperatures for the mixtures H-2 + O-2 in CO2 and N-2, between 1.0 and 300 bar and 288-348 K is presented. A group contribution equation of state (GC-EoS) has been selected to predict thermodynamic properties of the mixture, i.e. residual enthalpy, heat capacity and others, as well as phase equilibrium data, giving deviations lower than 10% at high pressures. The use of CO2 as a diluent increases the operational margin from 4.5 mol% H-2 at 1 bar up to ca. 7.0-9.0 mol% H-2 at 200 bar due to the increase in the heat capacity. On the other hand, the use of nitrogen or air as a diluent only increases the margin from 5.2 mol% H-2 at 1 bar up to ca. 6.0 mol% H-2 at 200 bar. (C) 2010 Elsevier B.V. All rights reserved.