Supercritical water oxidation (SCWO) of an aromatic chlorinated species, o-dichlorobenzene (o-DCB), is studied using a tubular flow reactor. o-DCB is often found in chemical waste streams and is similar to polychlorinated biphenyls (PCBs), an acute environmental hazard, in its physical-chemical properties. The experiments focus chiefly on the effect of temperature on the degradation efficiency of the SCWO process. Experiments are also performed for subcritical conditions. Molecular Dynamics simulations of OH radical and phenol in water are carried out in order to estimate the diffusion-controlled limit of the reaction between aromatic species and hydroxyl radical in aqueous solution. It is speculated that high diffusivity of the reacting species is a major factor responsible for high degradation efficiency of oxidation reactions in supercritical water. (C) 2005 Elsevier B.V. All rights reserved.