We have synthesized new electrocatalysts for the O2 reduction reaction that does not contain Pt. They consist of carbon-supported Pd-Fe alloys and have very high oxygen reduction. The nanoparticles with a Pd:Fe molar ratio of 3:1 (Pd3Fe/C) show a higher mass activity than that of commercial Pt/C. The surface-specific activity of the Pd-Fe alloys is related to the Pd-Pd bond distance: the shorter the bond distance, the higher the activity. This new class of electrocatalysts promises to alleviate some major problems of existing fuel cell technology by simultaneously decreasing materials cost and enhancing performance.