The kinetics of the self-reactions of benzyl and o-xylyl radicals was studied experimentally over the temperature range 295-800 K. The radicals were produced by the 248-nm photolysis of oxalyl chloride followed by the H-abstraction reactions from toluene or o-xylene by Cl atoms and detected by cavity ring-down spectroscopy. The visible absorption cross sections of the radicals were determined relative to that of the HCO radical. The rate constants determined were k(benzyl + benzyl) = 1.29 x 10 T-3(2.669) exp(-674/T) cm(3) molecule(1) s(1) (Delta log(10)k = +/- 0.096) and k(o-xylyl + o-xylyl) = 2.57T (3.784)exp(-1025/T) cm(3) molecule(1) s(1) (Delta log(10)k = +/- 0.107). (C) 2011 Elsevier B. V. All rights reserved.