A method for the surface area determination of platinum on 5% Pt/Al2O3 catalysts by electrochemically generated oxygen has been tested. This method is based on the oxidation of adsorbed hydrogen on a platinum surface area by oxygen that is generated electrochemically. The course of the titration was followed by measurement the potential of a catalyst suspended in a sulphuric acid solution. The applicability and the accuracy of this method were tested by a measurement of platinum particle sizes using XRD and electron microscopy. (c) 2007 Elsevier B.V. All rights reserved.