Surface oxides on smooth platinum, electrodeposited platinum black, and platinum black‐polytetrafluoroethylene molded electrodes have been characterized by anodic oxidation and cathodic stripping. The oxidation sequence for smooth platinum and platinum black electrodes is . At higher potentials smooth platinum forms and while platinum black forms . The initial oxidation of platinum to and subsequent reduction has been used as a basis for the determination of platinum electroactive surface areas. The formation of a “tight” structure on smooth platinum at higher potentials may account for some of the unusual properties of smooth platinum electrodes. The failure of platinum black to form tight may be due to irregular platinum atom arrangement and related to its catalytic properties.