Thermodynamic data of multicomponent brines are needed to properly treat brines from oil/gas and CO2 sequestration operations. Joule-heating treatment of hypersaline brine is a unique methodology that allows for direct heating of brines without the need of external heating, potentially simplifying operation and reducing process footprint. The thermodynamic properties of multicomponent hypersaline brine (> 3.5 wt%) are unknown and limited to estimations based on single component brine data. Experimental data for multicomponent brines at elevated temperatures and pressures do not exist due to operating conditions above the pseudocritical point of pure water. This study combines experimental results for multicomponent brines using a Joule-heated desalinator at pressures of 230 to 280 bar and temperatures of 387 to 406 degrees C with thermodynamic models previously created for single component NaCl brines to identify the deviations resulting from the additional species. In addition, a comparison between an Aspen Plus (R) v9 simulation using the ELECTNRTL model with experimental results is provided.