A significant fraction of the initial population of highly vibrationally excited oxygen molecules X (3)Sigma(g)(-)(v greater than or equal to 23) prepared by stimulated emission pumping, relaxes to much lower vibrational levels (Delta v approximate to-9). The time scale is much shorter than the known collisional lifetimes of the intervening vibrational levels and thus a sequential single-quantum relaxation mechanism can be explicitly ruled out. State-to-state measurements after preparation of v=28 and 30 provide the final-vibrational state population distribution resulting from relaxation of these two states. For v=28(30), at least 38%(7.9%) of the initially prepared population, undergoes multiquantum vibrational relaxation. The observed multiquantum relaxation explains, at least in part, the previously reported "dark channel" for relaxation of vibrational levels higher than v=26, but does not exclude the possibility of reactive scattering (forming ozone) for the remaining fraction of highly vibrationally excited molecules. We discuss possible explanations of this startling result including V-V energy transfer, V-E energy transfer, and complex formation.