Data on the thermodynamic description of Gd ₂ O ₃ -Y ₂ O ₃ -HfO ₂ system determined by high-temperature mass spectrometry at 2500 K were discussed using the Barker-Guggenheim statistical thermodynamic theory and the Redlich-Kister empirical approach to consider the accuracy and the possibility of further interpretation of the values found. A comparison was made of the results obtained on the basis of the indicated approaches with the aim of the most reliable optimization of the values of the excess Gibbs energy found in the system under consideration.