In this study, effects of the addition of small amounts of water electrolysis products on laminar premixed methane/air flames have been investigated using chemical kinetic simulation methods. The CHEMKIN kinetic simulation package was used with the GRI kinetic mechanism. Pollutant concentrations. flame speeds, temperature profiles and lean flammability limits of methane/air, methane/hydrogen/air and methane/hydrogen/oxygen/air systems were compared at different addition percentages and equivalence ratios from 1.4 to the lean flammability limit. The addition of 10-20% hydrogen in the fuel was found to have a small effect in improving flame speed and lean flammability limit properties. However, the addition of oxygen and hydrogen in the same ratio as is found in water was shown to be beneficial. Improvements in the flame speeds of methane/air mixtures by the addition of 10% hydrogen acid its associated oxygen were equivalent to the improvements obtained by the addition of 20% hydrogen only. In near stoichiometric mixtures, the addition of oxygen substantially increased the NOx concentrations, but for lean mixtures no increase in NOx was predicted. CO emissions were reduced when hydrogen displaced carbon-containing fuels. (C) 2001 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.