The data that were obtained by using a capacitance manometer system to measure the deviation from stoichiometry in nonstoichiometric cerium dioxide as a function of oxygen partial pressure at 800°C were analyzed along with existing data obtained at other temperatures. It was determined that, for values of log less than −2.4, the observed −1/5 dependence of the deviation from stoichiometry upon the oxygen partial pressure is due to the existence of doubly ionized nonstoichiometric vacancies along with the presence of charge compensating doubly ionized vacancies that are caused by Ca impurities. The mass action constants that were calculated for the defect reaction at various temperatures were then used to analyze the conductivity data that exists at corresponding temperatures. It was determined that the −1/5 dependence of the conductivity upon the oxygen partial pressure is also due to the presence of doubly ionized nonstoichiometric vacancies along with the existence of charge compensating doubly ionized vacancies caused by Ca impurities. Finally, it was also shown that, for values of log less than −2.4, not only is the mobility a function of temperature only, but also that the oxygen partial molal enthalpy change is independent of both temperature and composition.