Typically, oxidation of metallic nanoparticles is thought to proceed from the surface inwards, with the formation of an oxide shell surrounding a metallic core. The presence of oxygen atoms near the center suggests that under sufficiently oxidizing conditions, platinum nanoparticles can become completely oxidized throughout their entire volume. Various experimental studies have shown that this is most likely not the case for larger nanoparticles (> 2.0 nm). For smaller nanoparticles with diameters close or lower than 2.0 nm, previous studies suggest that core oxidation is possible under specific conditions. To further validate these claims and our results, three carbon black-supported Pt catalysts were prepared and characterized by XRD, TEM, and XAS (EXAFS) with the aim of determining average Pt-Pt and Pt-O distances and coordination numbers as a function of particle size distribution.