Considerable effects have been observed for the specific surface area of carbon black support on the fundamental properties of PtRu/C catalysts, such as metal particle size, extent of alloying and catalytic activity for the oxidation of methanol. Equimolar ethanolic solutions of Pt(NH3)(2)(NO2)(2) and RuNO(NO3)(x) and seven different carbon black supports with specific surface areas ranging from 29 to 802 m(2) g(-1) were used for the preparation of the catalysts by the co-impregnation method. COad stripping voltammetry was adopted for the investigation of the effects of the specific surface area of the carbon black on the catalytic activity of the PtRu/C catalysts as well as for the determination of the actual exposed surface area of the bimetallic particles. A size effect of the PtRu particles on the catalytic activity for the oxidation of methanol was also observed. (C) 2003 Elsevier Ltd. All rights reserved.