Electron emission as a result of the interaction of clusters with intense laser pulses is commonly understood in terms of direct and evaporative ionization processes. In contrast, we provide evidence here of an important role played by autoionization in intense field ionization of molecular oxygen clusters. Superexcited states are populated during the cluster expansion, and their autoionization is observed on a ns time scale. Decay processes on fs to ps time scales are obscured by energy exchange of the emitted electrons with the environment.