Abstract: The potential of the Wilson semiempirical method was illustrated in the calculation of the thermodynamic properties of both binary and ternary systems containing rare earth oxides from the data on the corresponding binary systems at high temperatures. An analysis was made of the possibility to calculate the energy parameters of the interaction between components using the coefficients of the Wilson equation, which were found for the first time, in binary oxide systems at high temperatures. By the examples of the Sm₂O₃–Y₂O₃–HfO₂, Sm₂O₃–ZrO₂–HfO₂, and Y₂O₃–ZrO₂–HfO₂ systems at temperatures above 2000 K using the data on the corresponding binary systems obtained earlier by high-temperature mass spectrometry, the excess Gibbs energy was calculated by the Wilson approach in comparison with the results obtained by the Redlich–Kister and Kohler methods. It was shown that the best agreement between the experimental and calculated values of the excess Gibbs energy of the above systems was observed in the case of using the Wilson method as compared to the Redlich-Kister and Kohler methods for the concentration ranges that are significantly remote from the binary systems.