The intermolecular potential of the quintet state of molecular oxygen dimer has been calculated using highly accurate ab initio calculations. Comparison with the best experimental intermolecular potential shows an excellent agreement for the equilibrium distances and binding energies of most geometrical configurations studied. Significant discrepancies occur for some configurations, most striking is the equilibrium distance for the global minimum and the binding energy of the linear configuration. Further analysis is realized by calculating the isotropic and anisotropic terms of the theoretical potential and comparing it with the experiment. (c) 2005 Elsevier B.V. All rights reserved.