The 7s sigma and 6p sigma superexcited Rydberg states of OCS belonging to series converging onto the (B) over tilde (2)Sigma(+) ionic limit have been successfully prepared by three-photon UV excitation, and their ensuing competing relaxation processes have been probed by a time-delayed IR ionization pulse. The time profiles of S+ ions, which encode their fragmentation mechanism, are only observable at high pump intensities, thus providing unique experimental identification of the neutral predissociation channel producing S* atoms. Benefiting from this feature and by comparison with the time behavior of OCS+ ions, three competing relaxation channels are identified: autoionization associated with both (X) over tilde (II)-I-2 and (A) over tilde (II)-I-2 ionic states; internal conversion to isoenergetic R-A states, the deactivation of which manifests as a picosecond decay in the time profile of OCS+ ions; picosecond neutral predissociation appearing as a nondecaying plateau in the time profiles of S+ ions.