Using ultrafast extreme ultraviolet pulses, we performed a direct measurement of the relaxation dynamics of neutral superexcited states corresponding to the Rydberg series of . An extreme ultraviolet attosecond pulse train was used to create a temporally localized Rydberg wave packet and the ensuing electronic and nuclear dynamics were probed using a time delayed femtosecond near-infrared pulse. We investigated the competing predissociation and autoionization mechanisms in superexcited oxygen molecules and found that autoionization is dominant for the low Rydberg states. We measured an autoionization lifetime of and for the and Rydberg state groups, respectively. We also determine that the disputed neutral dissociation lifetime for the vibrational level of the Rydberg series is .