The solid-state reaction between barium carbonate and rutile powders to form barium metatitane BaTiO₃ was studied by themogravimetric analysis, X rays, and microscopy. Phase-stability domains were drawn in a temperature -P_co2, diagram. The dependence of the reaction kinetics on P_co2, P_o2 or P_n2 is discussed. In particular, the rate continuously decreases when P_co2 or P_n2 increases, but it reaches a maximum as a function of P_o2. For given partial pressures of gases and temperature the kinetics curves (conversion degree vs.time) may be interpreted by a "hampered" -diffusion mechanism.