The substitution of up to 5% Ca2+for Ba2+in BaTiO3 results In a shill in the oxygen pressure dependence of the equilibrium electrical conductivity that is in the same direction as that caused by addition of acceptor impurities such as Al3+or Ca2+substituted for Ti4+. In contrast to the latter effect, however, the shape of the conductivity plot is not changed, the conductivity value at the conductivity minimum is not affected, and the amount of the shift increases with decreasing temperature of measurement. It is shown that the shift is primarily due to an increase in the enthalpy of reduction and a decrease in the enthalpy of oxidation as increasing amounts of Ba2+are replaced by Ca2+.