In this work, the explosion behavior of stoichiometric CH4/O-2/N-2/CO2 and H-2/O-2/N-2/CO2 mixtures has been studied both experimentally and theoretically at different CO2 contents and oxygen air enrichment factors. Peak pressure, maximum rate of pressure rise and laminar burning velocity were measured from pressure time records of explosions occurring in a closed cylindrical vessel. The laminar burning velocity was also computed through CHEMKIN-PREMIX simulations. It is shown that the main effect of CO2 is not on kinetics and diffusive transport rates, but rather on the specific heat of the mixture. When the CO2 content decreases the adiabatic flame temperature down to about 1500 K, the combustion rate decreases and flame extinction occurs. In the plane CO2 molar content-oxygen air enrichment factor, maps were built which allow identifying the conditions of stable flame and extinguished flame. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved