Oxidation and hydrolysis reactions of benzene in supercritical water were investigated thoroughly using experimental measurements Little to no reaction occurred without oxygen at temperatures between 530 and 625 degreesC for residence times up to 6 s. Oxidation reactions were studied at temperatures ranging from 479 to 587 degreesC, pressures of 139 to 278 bar, reactor residence times from 3 to 7 s, and with varying initial benzene concentrations from 0.4 to 1.2 mmol/L and oxygen concentrations from 40% of oxygen demand to 100% excess oxygen. To a 95% level of statistical confidence, the oxidation rate was found to be of 0.4 +/- 0.07 order in benzene, 0.17 +/- 0.05 order in oxygen, and 1.4 +/- 0.1 order in water, with an activation energy of 270 +/- 10 kJ/mol. The primary oxidation product at all reaction conditions studied was carbon dioxide. Other important oxidation products were carbon monoxide, phenol, and methane. Trace levels of additional light hydrocarbon gases and single- and multi-ringed aromatic species were also detected under some conditions.