Photooxidation of benzene at 254 nm has been studied in 10-KAr matrices. Both CO and CO2, which are believed to be secondary photodissociation products of initial peroxy-adducts or their dialdehyde isomers from the reaction of the triplet benzene with O2, were found to be the major observable oxidation products by IR analysis. Formation of these products has been studied as a function of photolysis time and of O2 concentration. On the basis of this result and estimates of transition state calculations, it can be concluded that at 2500K, the C6H6(T1) + O2 reaction is at least as important as the hydrogen abstraction reaction, C6H6 + O2 å C6H5 + HO2, for chain-initiation. The T1-state reaction is expected to be more important as its energy decreases for the larger members of the homologous series.