This report presents results of a study of desulfurization conditions (gas phase composition, temperature, and pressure) needed to prevent the formation of the by-product solid phases wustite, metallic iron, iron carbides, and elemental carbon in the high temperature desulfurization of coal gas by zinc ferrite. Chemical thermodynamic calculations of Fe/sub 3/O/sub 4/ reduction, iron carbide formation, and carbon deposition equilibria were made at incremental values of temperatures from 500/sup 0/ to 700/sup 0/ C and pressures from 1 to 20 atm. Laboratory experiments using solid-gas equilibration and thermogravimetric analysis confirmed the calculated phase boundaries. The phase boundaries were plotted on triangular C-H-O phase diagrams indicating the conditions of temperature, pressure, and gas composition needed to avoid the formation of unwanted solid phases. A computer program was written to interpolate the phase boundaries to intermediate temperatures and pressures. Inert substances such as nitrogen act primarily to dilute the C-H-O components of the gas phase. Zinc loss during desulfurization can be minimized by lowering the temperature, increasing the total gas pressure, and by using less chemically reducing coal gas compositions. 9 refs., 23 figs.