One of the key objectives in fuel-cell technology is to improve and reduce Pt loading as the oxygen-reduction catalyst. Here, we show a fundamental relationship in electrocatalytic trends on Pt(3)M (M=Ni, Co, Fe, Ti, V) surfaces between the experimentally determined surface electronic structure (the d-band centre) and activity for the oxygen-reduction reaction. This relationship exhibits 'volcano-type' behaviour, where the maximum catalytic activity is governed by a balance between adsorption energies of reactive intermediates and surface coverage by spectator (blocking) species. The electrocatalytic trends established for extended surfaces are used to explain the activity pattern of Pt(3)M nanocatalysts as well as to provide a fundamental basis for the catalytic enhancement of cathode catalysts. By combining simulations with experiments in the quest for surfaces with desired activity, an advanced concept in nanoscale catalyst engineering has been developed.