A multicomponent mole-fraction-based thermodynamic model has been fitted to osmotic coefficients, electromotive force measurements, degrees of dissociation of the HSO4 ion, differential heats of dilution, heat capacities, freezing points, and tabulated partial molal enthalpies of water for aqueous H2SO4, from 1200 to 328 K and from 0 to 40 mol kg(-1) at 1 atm pressure (1 atm = 101.325 kPa). The solution is treated as the mixture H+-HSO4-SO42--H2O. The equations yield a self-consistent representation of activities, speciation, and thermal properties which, for practical applications, is readily extended to more complex mixtures. Activity products of solutions saturated with respect to solid phases H2SO4.nH(2)O (where n is 1, 2, 3, 4, or 6.5) are determined as functions of temperature. Thermodynamic properties and speciation are tabulated at 253.15, 273.15, 298.15, and 323.15 K.