Oxy-fuel combustion of single coarse sub-bituminous coal char particle is investigated in an isothermal mass loss apparatus. Experimental studies are performed at the reactor temperature of 1100 K and in varying O-2 concen-trations of 42-60% in both O-2-CO2 and O-2-N-2 environments. A fully transient model is developed for the combustion and gasification reactions including the transport of heat and mass in the porous char particle and the gas film. The model is validated with experimental findings of the present authors as well as that reported in litera-ture over a wide range of O-2 concentrations. Simulation study is carried out to assess the effect of the particle size, the reactor temperature and the gas composition. The simulation shows that low diffUsivity of O-2 within the re-actor in CO2 environment and the endothermic gasification reaction are mainly responsible for lowering the peak temperature and the rate of combustion of char than that in O-2-N-2 environment. It is also observed that though the effect of CO2 on the combustion rate at low temperatures is insignificant, it is considerable at the reactor temperature of 1273 IC and above inO(2)-CO2 environment. The model is expected to provide vital information for re-actor design under oxy-fuel combustion and its integration with CFD analysis for identifying the optimum particle size, reactor temperature and oxygen concentration. (C) 2016 Elsevier B.V. All rights reserved.