Solubility and deposition rate experiments were performed in aqueous sodium sulfate and potassium sulfate solutions at elevated temperatures and pressures typical of the supercritical water oxidation (SCWO) process. The test cell was a six-port chamber in the form of a modified 1.91 cm (3/4 in.) diameter Swagelok cross with an internally heated cylinder (hot finger) mounted in its center. Solubilities were acquired by maintaining the surface temperature of the hot finger about 10degreesC above the gradually increasing bulk temperature of the solution flowing by it until salt precipitated on the hot finger. Solubility temperatures for sodium sulfate and potassium sulfate in water were measured for salt concentrations of up to 10% mass fraction. In the deposition rate experiments, the solution flowing past the hot finger was preheated to a temperature close to the solubility temperature and the salt layer-solution interface formed on the hot finger was maintained slightly above the solubility temperature to drive deposition. Deposition rates from SCWO streams containing up to 8% mass fraction salt were obtained by measuring the mass of the salt deposited on the hot finger after each (6 to 12 min) run. Solubility data are compared to those from other studies and a simple deposition rate model is developed and compared with the deposition rate data. Natural convection dominated transport and the system pressure was 25 MPa at all conditions. (C) 2004 American Institute of Chemical Engineers.