The reduction of oxygen on single phase Cu90Ni10 and Cu70Ni30 alloys in contact with 0.1 M borax at pH 9.2 has been investigated. The rate constant measured is independent of alloy composition for steady-state measurements. When the currents are measured in sweep experiments the current densities are larger for the alloy richer in nickel, indicating slow surface equilibrium processes. The value of n is 3.5 +/-0.2 for pre-reduced electrodes in a wide potential range, from -1.5 to -0.8 V versus the Hg \ Hg2SO4 \ K2SO4 (sat) electrode. The proposed reduction mechanism involves a bifurcation between a direct and a sequential mechanism involving O-2 chemisorbed on Cu(0). O 2001 Elsevier Science B.V. All rights reserved.