Molecular dynamics simulations are performed to study oxygen adsorption on platinum clusters supported on a graphite surface. The Sutton-Chen many-body potential is used for the Pt-Pt interaction, whereas a Steele potential was used to represent the carbon surface. The oxygen-oxygen intramolecular force is modeled by a harmonic oscillator model and other interactions are described by the Lennard-Jones potential. The results indicate an optimum loading of platinum for maximum specific adsorption of oxygen. Adsorption isotherms are constructed and the energies and orientation of adsorbed oxygen are reported. The relevance of this study to electrode processes is discussed.