The activities of a series of carbon-supported bimetallic catalysts, with different active phases loadings, were tested towards the oxygen reduction reaction (ORR). Pt was used in all materials and its loading was kept constant. Mo, W and Ru were used as promoting phases. Rotating Disk electrode experiments revealed that Pt-Ru displayed the best performance in oxygen reduction among the studied materials. The materials with the highest loadings of the second metal revealed the highest activities. X-Ray Diffraction studies (XRD) and Transmission Electron Microscopy (TEM) revealed the presence of homogeneously dispersed metallic ruthenium and different tungsten or molybdenum oxides in the corresponding catalysts. No evidence of alloying was found, and thus the catalytic performances appear to be related to the distribution and interaction of the active phases.