Pitzer-Li equation is employed for the evaluation of the thermodyna-mic properties of aqueous NaCl up to 823 K and 100 MPa

with maximum concentration of NaCl up to 65.2 wt%

which happens to be the saturation solubility of NaCl at the triple point. Thermodynamic properties evaluated include water activity

mean ionic activity coefficient of NaCl and Gibbs free energy. The calculated values correlate quite well with experimental data obtained. Parameters of short-range interparticle interaction (w) and Gibbs energies of NaCl fusion (△sG20/RT) over 623-823 K and up to 100 MPa required for such calculations are also presented. The changes of w with changes in temperatures are discussed. A reference pressure method is introduced to calculate the values of d

ρ and Ax for the Debye-Huckel term in PL equation at all lower pressures over the 623-823 K range and the reference pressures P

at different temperatures are also given.