The density and surface tension of the H2SO4/HNO3/H2O ternary system have been measured as a function of temperature from 245 to 298 K. The acid compositions range from 0 to 65 wt % for sulfuric acid and 0 to 45 % for nitric acid. The densities and surface tensions for the ternary system, combined with the data for the two binary mixtures water/nitric acid and water/sulfuric acid have been expressed as polynomials of the nitric acid and sulfuric acid weight % for the temperatures of 253 and 293 K. Since the densities and surface tensions vary linearly with temperature, data at temperatures other than 253 and 293 K can easily been obtained by interpolation. ¿ 2000 American Geophysical Union