A reduced dimensionality model is used to study the relaxation of highly vibrationally excited O-2(X (3)Sigma(g)(-),vgreater than or equal to20) in collisions with O-2(X (3)Sigma(g)(-),v=0). Spin-orbit coupled potential energy surfaces are employed to incorporate the vibrational-to-electronic energy transfer mechanism involving the O-2(a (1)Delta(g)) and O-2(b (1)Sigma(g)(+)) excited states. The transition probabilities obtained show a sharp increase for vgreater than or equal to26 providing the first direct evidence of the important role played by the electronic energy transfer processes in the depletion of O-2(X (3)Sigma(g)(-),vgreater than or equal to26). (C) 2004 American Institute of Physics.