We present a thermodynamic model based on electrolyte nonrandom two-liquid theory (eNRTL) for aqueous Ba2+-Na+-Cl--SO42- quaternary system. This study is part of a larger effort to develop an accurate and comprehensive thermodynamic model for high salinity produced water from oil and gas production. The quaternary system is one of the critical subsystems that cause scaling problems with high salinity brine solution. We obtain the eNRTL binary interaction parameters including their temperature dependence for the H2O:(Ba2+-Cl-) pair and the (Ba2+-Cl-):(Na+-Cl-) pair based on regression of available literature data. For the H2O:(Ba2+-SO42-) pair, the binary interaction parameters corresponding to the Debye-Huckel theory are adopted. The binary interaction parameters for the (Ba2+-SO42-):(Na+-SO42-) pair and the (Ba2+-Cl-):(Ba2+-SO42-) pair are considered to be zero. Further incorporating the eNRTL binary interaction parameters from the literature for the molecule-electrolyte pairs of H2O:(Na+-Cl-) and H2O:(Na+-SO42-) and the electrolyte-electrolyte pair of (Na+-Cl-):(Na+-SO42-), the model accurately calculates all thermodynamic and calorimetric properties for the quaternary system. In addition, it predicts reliably solubilities of barium sulfate and its scaling potential in the quaternary system. (C) 2017 Elsevier B.V. All rights reserved.