We report the interfacial tension between carbon dioxide and aqueous solutions of the mixed salt system (0.864 NaCl + 0.136 KCl) with total salt molalities between (0.98 and 4.95) mol.kg(-1). The measurements were made at temperatures between (298 and 473) K at various pressures up to 50 MPa by means of imaging a pendant drop of CO2-saturated brine surrounded by a water-saturated CO2 phase. The expanded uncertainties at 95 % confidence are 0.05 K in temperature, 70 kPa in pressure, and for interfacial tension gamma, the larger of 0.016 gamma and 0.6 mN.m(-1). The results of the study indicate that the interfacial tension increases linearly with the molality of the salt solution. An empirical equation has been developed to represent the present results as a function of temperature, pressure, and molality with an expanded uncertainty of 1.6 mN.m(-1).