The energy degradation of fast H and O atoms in H-2:O-2, CH4:O-2 and CH4:air mixtures is studied using Monte Carlo simulations, taking into account elastic collisions and chemical reactions. Based on the simulated results, the effect of high-energy atoms on the amount and composition of chemically active species produced in high-voltage pulsed discharges is estimated. The obtained results are used to consider the contribution of "hot" atom production to ignition and oxidation of fuel in combustible mixtures excited by nonequilibrium plasmas. It is shown that the presence of high-energy atoms leads to a decrease in the specific deposited energy required for plasma-assisted ignition and an increase in the density of products of plasma-assisted oxidation at gas room temperature. (C) 2016 The Combustion Institute. Published by Elsevier Inc. All rights reserved.