We present a time-dependent quantum mechanical investigation of predissociation of molecular oxygen following absorption in the Schumann-Runge continuum. We calculate the total and partial photoabsorption cross sections in a wave packet formalism in which the predissociation of the B (3)Sigma(u)(-) molecular state is attributed to spin-orbit interactions with the (1)Pi(u), a (3)Pi(u), (5)Pi(u), and 2 (3)Sigma(u)(+) repulsive states. We calculate the branching ratio, describing the relative rates of production of excited (D-1) and ground-state (P-3) oxygen atoms, and find close agreement with a recent measurement.