Acetic acid (CH3COOH) hydrolysis and oxidation in supercritical water were examined from 425-600 degrees C and 246 bar at reactor residence times of 4.4 to 9.8 s. Over the range of conditions studied, acetic acid oxidation was globally 0.72 +/- 0.15 order in acetic acid and 0.27 +/- 0.15 order in oxygen to a 95% confidence level, with an activation energy of 168 +/- 21 kJ/mol, a preexponential factor of 10(9.9+/-1.7), and an induction time of about 1.5 s at 525 degrees C. Isothermal kinetic measurements at 550 degrees C over the range 160 to 263 bar indicated that pressure or density did not affect the rare of acetic acid oxidation as much as was previously observed in the oxidation of hydrogen or carbon monoxide in supercritical water. Major products of acetic acid oxidation in supercritical water are carbon dioxide, carbon monoxide, methane, and hydrogen. Trace amounts of propenoic acid were occasionally detected. Hydrolysis or hydrothermolysis in the absence of oxygen resulted in approximately 35% conversion of acetic acid at 600 degrees C, 246 bar, and 8-s reactor residence time. Regression of the limited hydrolysis runs assuming a reaction rate first-order in organic gave a global rate expression with a preexponential factor of 10(4.4 +/- 1.1) activation energy of 94 +/- 17 kJ/mol.