The effect of the presence of singlet oxygen molecules O-2(a(1)Delta(g)) in a CH4-air mixture on the speed of laminar flame propagation is considered. The known experimental data on the laminar flame speed and ignition delay are used to validate the developed kinetic model involving electronically excited oxygen molecules O-2(a(1)Delta(g)) and O-2(b(1)Sigma(+)(g)). Numerical simulation shows that the presence of 10% O-2(a(1)Delta(g)) in molecular oxygen enables to increase significantly (by a factor of 1.7) the speed of flame propagation in a fuel-lean (phi = 0.45) methane-air mixture. The main reason for such an acceleration of flame propagation is the intensification of chain reactions due to addition of singlet delta oxygen molecules. For a fuel-rich mixture (phi = 1.9), the growth in the flame speed is significantly smaller and attains a factor of 1.4. (C) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.