Highly correlated ab initio calculations of the ground and low-lying electronic states of O-2 and O-4 together with a semi-empirical estimate of the spin-orbit coupling among them have been performed. For the diatomic, our calculations agree well with recent spectroscopic measurements. For the O-2(v = 0)-O-2(v) collision system, avoided crossings allow mixing of the electronic configurations with appreciable spin-orbit coupling into the lowest-lying excited states. As a consequence, spin-orbit transitions can occur at significantly lower vibrational energies of the O-2(v) moiety induced by collisions with O-2(v = 0). This mechanism must be partially responsible for the observed jump in depletion rates of O-2(v) determined experimentally,