An equation of state has been developed for the representation of the phase behavior of high-temperature and supercritical aqueous systems containing salts and nonelectrolytes. The equation includes a reference part that is based on a model for hard-sphere ion pairs and dipolar solvent molecules. In addition to the reference part, the equation contains a perturbation part, which is expressed by a truncated virial-type expansion. To enhance the predictive capability of the EOS for normal fluids such as hydrocarbons, the equation has been reformulated using the three-parameter corresponding-states principle. For salt-water systems for which little experimental information is available, a predictive procedure has been developed that relies on similarities in the fluid phase behavior of various salt-water systems. This procedure utilizes the equation of state for NaCl+H2O as a prototype system and introduces a transformation of parameters for the salt of interest. The equation accurately represents vapor-liquid equilibria, solid-liquid equilibria and densities for systems containing water, salts and hydrocarbons.