The kinetics of electrochemical formation and dissolution of oxygen in the electrolysis of molten potassium bisulphate in the temperature range of ca 230–330°C has been studied. The potentiostatic and galvanostatic polarization curves at high overvoltages fit a Tafel equation. The anodic slope is RT/F, and the cathodic slope RT/2F. At low anodic overvoltages oxide-film formation seems to occur on the platinum. In the cathodic overvoltage region dissolution of oxygen occurs with a well defined limiting cd related to the amount of oxygen dissolved in the melt. Non-steady measurements for the anodic reaction yield kinetic parameters which coincide with those obtained from polarization curves. Experimental capacitances have reasonable low values. Anodic results are discussed in terms of the discharge of sulphate or bisulphate ions on a totally oxidized platinum surface, the rate-determining step being a two-electron transfer. The cathodic reactions comprise a diffusion process related to oxygen dissolution and the already known electrochemical formation of hydrogen.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas