Three samples of pregraphitized carbon blacks with the same porous texture but increasing amounts of oxygen surface groups have been used to prepare carbon-supported platinum catalysts (about 1 wt % loading). The carbon surface becomes oxidized upon impregnation with hexachloroplatinic acid in aqueous solution, whereas platinum is reduced from Pt(IV) to Pt(II), as evidenced by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) experiments. TPD profiles of fresh catalysts show a peak of carbon monoxide evolution at low temperatures (623-723 K) which does not appear in those of the parent supports, pointing out decomposition of the oxygen surface groups created upon impregnation with the metal precursor. The platinum-support interaction in the reduced catalysts is diminished by the presence of oxygen surface complexes, leading to a lower metal dispersion and a lower resistance to sintering.