Electrical conductivity measurements have been made in the system as a function of composition, temperature, and oxygen pressure. At 1600°C, can dissolve about 16 m/o which leads to the creation of anion vacancies. These defect solid solutions behave as oxygen anion conductors below an oxygen pressure of 10−7 atm. Above this pressure, the appearance of p‐type conductivity, proportional to , produces a region of mixed conduction. No evidence of n‐type conductivity was observed. Even exhibits predominantly ionic conduction at intermediate oxygen pressures. Several transport numbers were verified by emf measurements. The results of this investigation are compared with those obtained previously for other oxide electrolyte systems.