Iron oxysulfide as a relative low melting-point liquid is a potential desulfurizing agent for high-sulfur fuel gases originating from the gasification of high-sulfur coals. Desulfurization is accomplished by injecting magnetite (Fe3O4) into sulfur-bearing reducing gases which would originate upon gasification of coal. The sequence of steps for desulfurization includes reduction of magnetite to wustite followed by an exchange between the oxygen in wustite with sulfur from the fuel gas. As this reaction proceeds, melting occurs. The rate-limiting step in the first stage of the process, as followed by thermogravimetric analysis (TGA) which measures the weight loss associated with the phase change from magnetite to wustite, is controlled by the chemical reaction kinetics of reduction. Following reduction, the rate-limiting step in the second stage of the process as measured by sample weight gain (exchange of sulfur for oxygen) is shown to be controlled by interdiffusive mass transport in the liquid phase. For temperatures in operating gasification systems above 1400 degrees C, extrapolation of the TGA data using a kinetic model for fine particles indicates that a high degree of desulfurization is possible at residence times of less than one-second.