Regression of experimental activity coefficient and dissociation constant data reported in the literature with the Huckel (1925) and Setchenow (1892) equations (Helgeson et al., 1981) and the revised HKF equations of state (Tanger and Helgeson, 1988; Shock et al., 1989, 1992) generated parameters and thermodynamic properties of dissociated KCl and KCl 0 at 25°C and 1 bar that can be used to calculate the standard partial molal thermodynamic properties of KCl 0 and the activity coefficients of KCl at temperatures and pressures to 1000°C and 5 kbar.