The rotating disc electrode-PSC technique and cyclic voltammetry were used to study the reduction reaction of oxygen on a gold electrode in alkaline solution. The adsorbed intermediate on the electrode and the soluble intermediate near the electrode surface were measured quantitatively by using these techniques. The mechanism of this reaction is postulated by analysing the experimental results thus obtained. The data seem to support the existence of the adsorbed intermediate HO2-(1+lambda), with 0.07 less than or equal to lambda less than or equal to 0.32.