The influence of additives of various chemical natures (CH4, N-2, CO2, and steam) at a laminar burning velocity S-u of hydrogen in air has been studied by numerical modelling of a flat flame propagation in a gaseous mixture. It was found that the additives of methane to hydrogen-air mixtures cause as a rule monotonic reduction in the S-u value with the exception of very lean mixtures (fuel equivalence ratio (phi = 0.4), for which a dependence of the laminar burning velocity on the additive's concentration has a maximum. In the case of the chemically inert additives (N-2, CO2, H2O) the laminar burning velocity of rich near-limit hydrogen-air flames drops monotonically with an increase in the additive's content, but no more than 1.5 times, and the adiabatic flame temperature changes slowly in this case. In the case of methane as the additive, the laminar burning velocity is diminished approximately 5 times with an increase in the adiabatic flame temperature from 1200 to 2100 K. Deviations from the known empirical rule of the approximate constancy of the laminar burning velocity for near-limit flames are shown. (C) 2009 Elsevier Ltd. All rights reserved.