The kinetics of O-2 reduction has been examined on an ink-type electrode made with Pt supported on high-area carbon. Electrocatalysts with 5-40 mass % of Pt on Black Pearls, Vulcan XC-72, and Shawinigan acetylene black carbons were used. Experiments were performed in 0.1 M solutions of H2SO4, H3PO4, HClO4, and NaOH. Kinetic parameters of O-2 reduction were found to be similar as on a smooth Pt surface. No influence of the type of carbon was observed. The mass activity of O-2 reduction was independent of Pt loading at low currents, but at high currents the mass activity decreased with an increase in Pt loading. It is suggested that mass-transfer limitations are responsible for the different influence of Pt loading on mass activity at low and high currents. Reproducibility of the measurements on the ink electrode was satisfactory, and it is recommended for investigations df dispersed electrocatalysts.