Electrochemical oscillatory phenomena have been observed in the redox reaction of the O-2/O-2(-) (superoxide ion) couple on a hanging mercury drop electrode (HMDE) in a limited aprotic medium. The current oscillation occurs during the reoxidation process of the electrogenerated O-2(-). It has been found that the observed oscillation is really irregular, complicated and affected by the addition of poly(vinyl chloride) as a maximum suppressor as well as many other experimental factors such as solvent, electrode substrate, concentration of O-2(-) in the electrode vicinity and potential scan rate in cyclic voltammetry. The oscillation phenomena have been explained similarly to the maxima in classical polarography (i.e. by streaming phenomena) and in addition, based on the formation-destruction of a passive film on the electrode surface which results in the dissolution of the mercury electrode. The results obtained demonstrate that the electrogeneration and adsorption of O-2(-) on HMDE are indispensable for the present oscillation.