As part of the effort to develop a comprehensive molecular thermodynamic model for high salinity produced water based on the electrolyte nonrandom two-liquid theory, this work presents the model results for the aqueous Na+-K+-Mg2+-Ca2+-SO42- quinary system. With the binary interaction parameters fully parameterized for the water-electrolyte pairs and the electrolyte-electrolyte pairs, the model satisfactorily describes the thermodynamic properties for the aqueous quinary system and its binary, ternary, and quaternary subsystems for the temperature range 273.15-473.15 K and the salt concentrations up to saturation. The model results are compared with the salt solubility and thermodynamic data available for the subsystems with special attention to systems involving (Ca2+ SO42-). (C) 2019 Elsevier B.V. All rights reserved.