Four ternary catalysts, Pt-Ag-Ru, Pt-Au-Ru, Pt-Rh-Ru, and Pt-Ru-W2C, were investigated as anode electrocatalysts for oxidation of hydrogen-containing carbon monoxide. These catalysts were either alloys or intimate admixtures of the components. Membrane electrode assemblies were prepared for all the catalysts with anode Pt loading of 0.4 mg/cm(2), and anode polarization was determined for oxidation of a H-2 stream containing 104 ppm CO. Potentials for CO oxidation were determined by stripping preadsorbed CO using cyclic voltammetry. The Pt-Ru-W2C (1:1:0.4 molar ratio) oxidizes CO at a lower potential, and the polarization for oxidation of hydrogen-containing CO was lower than the widely used Pt-Ru (1:1 molar ratio) catalyst. At low polarization, the Pt-Ru-W2C catalyst showed twice the activity of the Pt-Ru catalyst when the oxidation currents were normalized to the Pt area. (C) 2003 The Electrochemical Society.