This paper reports an investigation on the effect of the surfactant aliquato(R) 336 (A336) on the mass transport parameters of the oxygen reduction reaction and on H2O2 electro-generation rate. Results have shown that most of the positive effects of adding A336 to the electrolyte are observed at concentrations around the critical micelle concentration (CMC). Results analyzed in this paper have shown that adding A336 at CMC shifted half-wave potential for 02 reduction by 80 mV more negative and, furthermore, extended limiting current plateaus for the reaction O-2 --> H2O2 over extra 100 mV more negative. Limiting currents for 02 reduction are higher in the presence of A336, and the O-2 diffusion coefficient increased from 2 x 10(-6) CM2 s(-1) to 9 x 10(-6) cm(2) s(-1). All these findings were verified by controlled potential electrolysis in a flow electrochemical reactor, where it was also found that the H2O2 electro-generation rate reached a maximum for A336 concentrations close to the CMC. (C) 2007 Elsevier B.V. All rights reserved.