Hydrothermal oxidation is an efficient and clean way for the treatment of wastewater containing organic matter. Because of its specific properties, supercritical water ensures high conversion of a wide range of organic load in the presence of an oxidant. The purpose of this work is to develop a mathematical model for a continuous flow tubular reactor devoted to hydrothermal oxidation. This reactor has a low ratio diameter length with one air injection. The mathematical model is based on plug flow assumption. The governing equations are: momentum, mass, species and energy balances. According to this model. the profiles of temperature and concentration of chemical species are computed along the reactor. The numerical predictions of the model are compared to experimental profiles obtained in the case Of supercritical oxidation of phenol. These comparisons show very good agreement. (C) 2009 Elsevier B.V. All rights reserved.