Thermal characteristics and kinetic parameters of rice straw (RS) and sawdust (SD) raw materials were investigated under an oxidizing atmosphere using a non-isothermal thermogravimetric analysis (TGA). The effect of H2O and CO2 on the oxy-steam combustion was studied by performing the TGA experiments using a mixture of (O2/CO2/H2O/N2) at different compositions. Kinetic parameters were determined using a volumetric model (VM), random pore model (RPM), double parallel random pore model (DRPM), mixed volumetric random pore model (MVRPM) and a new proposed double parallel volumetric model (DVM). The good fit between the experimental and modeled data was obtained from the parallel and mixed models results when the fractional conversion was used in these models. While the models’ solutions didn’t fit with the experimental results when they were solved based on the conversion rate. The new proposed DVM model gave the best fit with experimental conversion (a). The ignition delayed at high concentration of H2O due to the highest specific heat of H2O that lowered the temperature of the fuel particles. The activation energy and the frequency factor of RS were lower than that of SD. The char conversion rate of SD exceeded that of RS.