A voltammetric study is described of conditions governing the production and stability of anodically formed bulk oxide on Pt in dilute . The range of anodizing conditions covered in 1 or was: current‐density, up to 10 A/cm2; temperature, 11°–93°C; duration, up to 18 hr. The oxidizability of the Pt anode (with respect to formation of bulk oxide) was subject to considerable hysteresis. Provided a potential of about 2.15V, RHE was exceeded, electrode oxidizability seemed to be controlled largely by the amount of strain energy present in the Pt surface. The electrolytic formation and reduction of thick bulk oxide layers effected large increases in electrode roughness factor (up to 100X or more).