Oxy-fuel combustion processes involve high CO2 partial pressures. Therefore, gasification reactions of carbonaceous materials with CO2 may take place in addition to reactions with O2. A thermodynamic analysis of both reactions was carried out through electronic structure calculations in order to evaluate the previous hypothesis. In most cases, the evaluated CO2 adsorption reactions are thermodynamically favorable, while CO evolution reactions from oxidized carbonaceous material are endothermic although exergonic at high temperatures. Our results indicate that simultaneous occurrence of combustion and gasification reactions is possible, at least from a thermodynamic point of view.