The kinetics of the oxidation of dense pellets of CaS by the reaction: $$2CaS(s) + 3O_2 (g) \to 2CaO(s) + 2SO_2 (g)$$ was examined by continuous thermogravimetric analysis. The experiments covered a temperature range of 1673 to 1853 K, Ar-O2-SO2 mixtures varying from 1 to 40 pct O2 and 0 to 20 pct SO2, and gas velocities ranging from 20 to 57 cm/s at the reaction temperature. Analysis of the data shows that the initial rate of the reaction is controlled by the mass transfer of O2 through the gaseous boundary layer of the pellet and is subsequently controlled by the diffusion of O2 through the porous layer of the reaction products. To verify these results, the permeation rates of SO2 through the reaction products were measured at room temperature and compared to values calculated from the thermogravimetric data.