To develop a new process for removing high-concentration SO2 from industrial flue gases, the carbothermal reduction of SO2 by oil-sand fluid coke at 700 degrees C was investigated by varying the inlet concentration of either O2 or H2O. Concentrations of O2 and H2O ranged from 0 to 20% and from 0 to 30%, respectively, in a stream of SO2 (18%) with the balance helium. Addition of O2 and H2O was found to enhance SO2 reduction. The enhancement was attributed to the reducing gases, CO and H2, produced by solid-gas reactions between carbon and O2 or H2O. The effects of O2 and H2O on sulfur yield, however, were bifacial: adding O2 and/or H2O increased the sulfur yield when SO2 conversion was incomplete, otherwise, it decreased the sulfur yield through the formation of sulfides such as H2S. The results of a thermodynamic analysis were in a good agreementwith the experimental results, suggesting that gas-solid reactions were slow enough to allow gas-phase equilibrium. This study indicates that carbon, such as oil-sand fluid coke, can be utilized to remove SO2 in flue gases containing O2/H2O and to convert it to elemental sulfur.