The oxidation of phenol in aqueous solution was studied in a semibatch reactor at temperatures between 170 and 220 degreesC and at pressures of 5.10-10.15 MPa. The reaction showed an induction period followed by a rapid degradation. During the rapid step, the oxidation reaction was first-order in each phenol and oxygen, with an activation energy of 67.4 +/- 9.8 kJ mol(-1). The kinetic constant depended on the concentration of organics represented by the initial concentration of phenol. A series of consecutive runs without removal of the products showed a progressive acceleration of the reaction and a suppression of the induction period. The length of the induction period was studied following the model of Willms et al. (Willms, R. S.; Balinsky, A. M.; Reible, D. D.; Wetzel, D. M.; Harrison, D. P. Ind. Eng. Chem. Res. 1987, 26, 148). The activation energy of the induction period was 56 kJ mol(-1) for reactions below 190 degreesC and 170 kJ mol(-1) for higher temperatures, which probably indicates a change in mechanism. The results from reactions performed without removing reaction products suggest that the accumulation of intermediate compounds could explain the observed increase in the rate constant from run to run.