The use of ammonium nitrate as an oxidizing agent in hydrothermal oxidation of organic compounds was investigated. The oxidation of model compounds, methanol, acetic acid, and phenol, was studied at 500 degrees C and 345 bar. High organic, ammonia, and nitrate removal was achieved at stoichiometric concentrations. The oxidation of ammonia by nitrate was much faster than the oxidation of either methanol or acetic acid and only slightly faster than phenol. Nitrogen products included N-2, N2O, and NO2- as well as toxic NO and trace amounts of NO2. Carbon products were CO2, HCO3-, CO32-, and CO. The co-oxidant system with hydrogen peroxide and ammonium nitrate was studied to eliminate the NOx production. Stoichiometric concentrations of hydrogen peroxide to the carbon concentrations resulted in undetectable NOx levels.