Analysis of the autothermal wet oxidation of dilute aqueous wastes reveals some important differences between the subcritical and supercritical operation of this process. The energy requirements are considerably higher for supercritical operation and are comparable to those for incineration. The calculations show that the efficiency of the heat exchanger in the near-critical region decreases significantly and using a regenerative heat exchanger for supercritical operation requires excessive heat-transfer area even for wastewaters with heating values around 1000 kJ.kg-1. Better results are obtained at higher pressures. This study demonstrates that autothermal operation of the supercritical wet oxidation process for dilute wastewaters is feasible only with the addition of auxiliary fuel.