The laminar burning velocities of hydrogen-methane/air mixtures at NTP conditions were calculated using the CHEMKIN PREMIX code with the GRI kinetic mechanism. The equivalence ratio and the fuel composition were varied from lean to rich and from pure methane to pure hydrogen, respectively. The results show that the values of the blends laminar burning velocities are always smaller than those obtained by averaging the laminar burning velocities of the pure fuels according to their molar proportions. Moreover, in lean mixtures the hydrogen addition enhances the methane reactivity slightly, while a strong inhibiting effect of the hydrogen substitution by methane is observed at rich conditions. These findings are attributed to changes of both, the H radicals concentration and the reactions involving such atoms. It was attempted to correlate the calculated laminar burning velocities by means of a Le Chatelier's Rule-like formula. A good prediction is obtained, except for rich mixtures With high hydrogen contents. With this limitation, the proposed formula is Successfully applied also to mixtures at higher than normal values of initial pressure (up to 10 atm) and temperature (up to 400 K). (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.