The rate constant of the reaction OH + CH3O2 -> products (R1) has been measured at 294 K by simultaneous coupling of Laser Induced Fluorescence (LIF) and cw-Cavity Ring Down Spectroscopy (cw-CDRS) to laser photolysis. OH radicals were generated by 248 nm photolysis of either H2O2 or O-3 in the presence of H2O, CH3O2 radicals were generated simultaneously by photolysis of CH3I and their absolute concentrations were obtained by cw-CRDS. OH decays were measured under excess CH3O2 concentrations and a very fast rate constant of k(1) = (2.8 +/- 1.4) x 10(-10) cm(3) s(-1) was found independent of pressure at 50 and 100 Torr helium. (C) 2013 Elsevier B.V. All rights reserved.