Enthalpies of formation of many ternary uranium oxides were determined by solution calorimetry by O'Hare, Cordfunke, and others between 1967 and 1988, These authors achieved accurate results by using pure starting materials, synthesizing nearly phase-pure crystalline products, developing appropriate thermochemical cycles, and controlling calorimetric conditions. Their studies provided a foundation for subsequent calorimetric studies of ternary lanthanide and actinide oxides with alkali and alkaline earth elements. These studies generated a substantial thermochemical database for the ternary oxides of transition metals, lanthanides, and actinides. In this paper, the stability of several families of ternary actinide oxides is correlated in terms of the enthalpy of reactions such as AO(s) + BO2(s) = ABO(3)(s) (AO = alkaline earth oxide, BO2 = oxide of tetravalent actinide) combined with an acidity scale for binary oxides that is based on the enthalpies of formation of the oxides. The success in correlating of enthalpies of formation of ternary actinide oxides with oxide acidities enhances the value of well-determined experimental thermochemical and structural properties of these materials.