A potential energy surface for the Ar(S-1)+O-2(X (3) Sigma(g)(-)) interaction is calculated using the supermolecular unrestricted Moller-Plesset (UMP) perturbation theory and analyzed via the perturbation theory of intermolecular forces. The global minimum occurs for the T-shaped geometry, around 6.7 a(0). Our UMP4 estimate of the well depth of the global minimum is D-e = 117 cm(-1) and the related ground state dissociation energy obtained by diffusion Monte Carlo calculations is 88 cm(-1). These values are expected to be accurate to within a few percent. The potential energy surface also reveals a local minimum for the collinear geometry at ca similar to 7.6 a(0). The well depth for the secondary minimum at the UMP4 level is estimated at D-e = 104 cm(-1). The minima are separated by a barrier of 23 cm(-1). The global minimum is determined by the minimum in the exchange repulsion in the direction perpendicular to the O-O bond. The secondary, linear minimum is enhanced by a slight flattening of the electron density near the ends of the interoxygen axis.