An energetic beam of Xe atoms causes the dissociation of adsorbed O-2 molecules on cold Ag(110) or Pt(111) surfaces. This is a parallel channel to the previously observed collision induced desorption. Using EELS, mass spectrometry and TDS, the energy dependence of the collision induced dissociation and desorption cross sections was measured over a range of Xe beam energies, On both surfaces these events seem to have a common threshold energy of about 0.9 eV for Ag(110) and 1.2 eV for Pt(111). The branching ratios between desorption and dissociation, which are about 3 and 3.3 for Ag(110) and Pt(111), respectively, exhibit no or weak energy dependence.