Oxygen reduction proceeds on copper electrodes in boric + borate buffer by the four electron pathway. Difference reflectance spectroscopy shows that surface oxide species are formed during oxygen reduction on pre-reduced copper. The redox couple Cu2O/CuO plays an important role in the reduction sequence and a CE mechanism is proposed, although direct electron transfer to the oxygen molecule from oxide-free surfaces appears possible. In this case, the behaviour of copper is similar to that of the isoelectronic metal gold.