Wastes that can be treated by supercritical water oxidation often contain salts. Salts are almost insoluble under supercritical conditions and can result in severe fouling. A simple heat- and mass-transfer model was developed and tested experimentally for sodium sulfate in a fully turbulent flow of water at 25 MPa. This model uses empirical heat-transfer correlations to estimate mass-transfer rates. The diffusion coefficient of the salt is calculated from the Stokes-Einstein relation using a hydrodynamic diameter of 2 to 6 Å. New measurements of solubility showed that the solubility of sodium sulfate decreases by a factor of about 1,000 as the temperature increases from 380°C to 400°C. Salt deposition rates, inferred from the outside temperature of a heated test section, were reasonably close to the model predictions.