The homogeneous degradation of benzene (B), toluene (T), ethylbenzene (E) and p-xylene (X) (BTEX) was studied in aqueous solutions, at pH 3.0, of hydrogen peroxide (5.8 mM) under UV irradiation in a photoreactor equipped with a 300 nm lamp of light intensity 3.5 x 10(-5) Ein L(-1)min(-1). BTEX was substantially degraded by the H2O2/UV system, with >90% disappearing in 10 min of irradiation. The decomposition of BTEX was studied either as single or as multi-component systems. The effects of irradiation time, amounts of H2O2 in molar ratios, rate of degradation and competition between components were thoroughly examined. It can be stated that the rate of BTEX degradation in mixture was higher than those for the individual components due to external effects of the absorption of UV fight by the mixture, and their effects on enhancing the formation of OH. radicals. The appropriate figure of merit, the electrical energy per mass (EE/M), was estimated at various molar ratios and it was confirmed that the best value was the one depicted for p-xylene (0.065 kWh kg(-1)). A theoretical model for the degradation pathway was proposed. (C) 2004 Society of Chemical Industry.