Near UV-illuminated slurries of titanium dioxide were used to study the photocatalyzed degradation kinetics of benzene and perchloroethylene (PCE) as water contaminants. In all runs, the concentration(s) of reactant(s) (initially 15–500 μM) as well as the evolution of CO2 final product were monitored. The single component initial rate data were well described by Langmuir-Hinshelwood rate forms, and integration of these rate equations provided simulations of the entire time course of each reaction. Perchloroethylene degraded completely without any evidence of kinetically significant chemical intermediates; however, adequate simulation of the benzene time course data required the incorporation in the model of at least two reaction intermediates. Subsequent GCMS analysis of a benzene reaction slurry revealed several intermediate species, with positive identification of phenol and quinone. Using the kinetic rate parameters obtained from the single component initial rate data and including competitive intermediate terms, the Langmuir-Hinshelwood rate form was able to simulate the results of several binary reactant experiments. The data showed that the effect of PCE concentration on benzene reaction rate was negligible, while benzene and its intermediates significantly inhibited PCE degradation. Simulations with this simple model for diminution of both reactants as well as CO2 product evolution were quite good for low initial reactant concentrations, but overestimated the competitive inhibitory effect of high (≈ 300 μM) initial PCE concentrations.