A thermodynamic analysis of gasification of carbonaceous feedstocks using carbon dioxide and a mixture of carbon dioxide with steam or oxygen is carried out using Gibbs minimization approach. Simulations are carried out to study the effect of different operating conditions on the gasifier performance using Aspen Plus. Gasification using CO 2 at ambient conditions is not favorable under adiabatic condition. Complete carbon conversion can be obtained by increasing the operating temperature or flowrate of carbon dioxide. A cold gas efficiency greater than 1 is obtained under certain operating conditions. Maximum carbon dioxide conversion is obtained at the carbon boundary point. Based on the minimum energy requirement for complete carbon conversion, a universal optimal operating temperature of 850°C has been identified for gasification of any feedstock. Biomass requires less heat input compared to coal. Use of steam or oxygen as a cogasifying agent reduces the carbon dioxide and energy requirement but reduces carbon dioxide conversion. Syngas with a wide ranging ratio of hydrogen/carbon monoxide can be obtained using carbon dioxide gasification. Trends of simulation predictions are qualitatively consistent with experimental observations. © 2012 Elsevier Ltd.