A model based on dilute solution theory is extended to Henry's constants of gases and volatile organic compounds in aqueous solutions, with and without added salts. The model is applicable to salt solutions over significant ranges of temperature, pressure, and salt concentration, up to the solubitity limit of the salts considered in this work. Extrapolation over a range of salt concentrations requires one salt-dependent parameter, which can be approximated by the Setchenov constant at 298 K. As a result, literature or predicted values of Setchenov constants at a single temperature can be used to obtain Henry's constants over a range of temperatures and salt concentrations. Extrapolation in pressure was achieved using an expression that is similar to the Krichevsky-Kasarnovsky equation, with the partial molar volume of the gas or VOC at infinite dilution in water treated as an adjustable parameter. Regressed values of this parameter were found to be in good agreement with experimental partial molar volumes for methane + water and methane + water + salt systems at pressures up to 1000 bar. Therefore, it appears feasible to extrapolate Henry's constant data for gases or VOCs in water to aqueous salt solutions over significant ranges of pressures, temperatures, and salt concentrations, provided data on the Setchenov constant at 298 K and the partial molar volume of the VOC at infinite dilution in water are available. (c) 2005 Elsevier B.V. All rights reserved.