The oxidation of methanol and sodium borohydride (NaBH 4 ) on supported colloidal Os and Os-alloys (i.e. Os–Sn, Os–Mo and Os–V) have been studied by voltammetry and chrono-techniques (i.e., potentiometry, amperometry). The electrolytes were: 0.5M H 2 SO 4 for methanol oxidation and 2M NaOH (without and with 1.5×103M thiourea (TU)) for borohydride oxidation, respectively. Voltammetry results showed that the investigated Os-based materials were catalytically inactive with respect to methanol oxidation, contradicting therefore, the theoretical suggestion by Kua and Goddard [J Am Chem Soc 1999; 121:10928–41] indicating electrocatalytic activity for Os toward methanol oxidation. Regarding the oxidation of borohydride, for direct borohydride fuel cells, preliminary results showed a voltammetric wave, with oxidation potentials between 0.1 and 0.3V vs. Ag/AgCl, KCl std , which were attributed to borohydride and TU oxidation. Chronopotentiometry results of Os-alloys showed a more positive operating potentials compare to colloidal Os catalysts.