Carbon-supported binary PtRu electrocatalysts were prepared by coimpregnation using ethanolic solutions of Pt(NH 3 ) 2 (NO 2 ) 2 as the Pt source, various Ru sources [RuCl 3 , Ru 3 (CO) 12 , and RuNO(NO 3 ) x ], and carbon black by thermal decomposition under reducing conditions, and their structure, morphology, and electrocatalytic properties were investigated. X-ray diffraction analysis and high resolution scanning electron microscopy indicated that the use of Cl-free Ru sources, i.e., Ru 3 (CO) 12 or RuNO(NO 3 ) x , afforded highly dispersed and uniform PtRu nanoparticles. Surface area measurements conducted by electro-oxidation of preadsorbed carbon monoxide indicated that the use of Ru 3 (CO) 12 as the Ru source yielded high surface area catalysts. In terms of the surfacearea specific current density (current density normalized by the specific surface area of PtRu metal obtained from preadsorbed CO electro-oxidation measurements), the electrocatalytic activity of Pt(NH 3 ) 2 (NO 2 ) 2 -Ru 3 (CO) 12 and Pt(NH 3 ) 2 (NO 2 ) 2 -RuNO(NO 3 ) x were equal. PtRu/C electrocatalysts prepared from ethanolic solutions of Pt(NH 3 ) 2 (NO 2 ) 2 -Ru 3 (CO) 12 resulted in high mass-specific activity toward methanol oxidation, with mass-specific current density as high as 159 mA mg Ϫ1 Pt at 500 mV. The efficiency of PtRu/C electrodes is discussed based on the significance of the use of Cl-free Ru sources.