The Fe-O-Zr, Cr-O-Zr, and O-Sn-Zr ternary systems have been modeled using the CALPHAD (CALculation of PHAse Diagrams) method to develop comprehensive thermodynamic descriptions essential for applications in nuclear materials and corrosion science. Experimental data from the literature and Density Functional Theory (DFT) calculations were used within this work to determine accurate thermodynamic parameters for the phases involved. The binary O-Zr system, common to all three ternary systems, was reassessed using ionic models to accurately describe the non-stoichiometry of zirconium oxide phases, which is crucial for predicting phase equilibria and material properties. To validate and refine our thermodynamic models, we conducted experimental studies specifically on the Cr-O-Zr system, and the resulting data were incorporated into our assessment to enhance its reliability and accuracy.