Pt/Pd is unusually active for formic acid electro-oxidation. While the oxidation of formic acid on Pt and Pt/Ru is poisoned by CO, the electro-oxidation of formic acid on Pt/Pd is not greatly inhibited by adsorbed CO. We examined CO stripping in the presence of formic acid and observed that the formic acid provides a continuous source of CO on Pt, Pt/Pd, and PtRu. CO stripping is slower on Pt/Pd than on the other catalysts even though Pt/Pd is unusually CO tolerant. Therefore, it is suggested that formic acid electro-oxidation occurs on a reaction site that is not inhibited by CO. (C) 2004 The Electrochemical Society.