Supercritical water oxidation has become a well-known treatment technology for conversion of aqueous wastes. By introducing a catalyst higher conversion and selectivity to carbon dioxide can be achieved at a lower- temperature and at shorter residence times. The stability of chromium oxide in supercritical water was studied to determine the feasibility of using catalysts during supercritical water oxidation. Various process variables, including oxygen and water concentrations, fluid flow rate, and temperature were found to affect the reactivity of the chromium oxide catalyst. Under these conditions, chromium was present in the reactor effluent as chromic acid, H2CrO4. The visual observation of the catalyst after the completion of the experiments suggested that a reaction front moved along the length of the reactor. A rate expression, based on Langmuir-Hinshelwood kinetics, with dissociative chemisorption of oxygen on a hydrated chromium oxide surface was proposed. The model, developed based on this rate expression and the continuity equation for the fluid phase, was consistent with the experimental results.