We report the branching ratios, phi, for photodissociation of O-2(-) in water clusters, O-2(-).(H2O)(n), as a function of excess energy [over the bond energy, E(excess) = hv - D-0(O-2(-))] and cluster size, 1 less than or equal to n less than or equal to 33. The two-dimensional phi(E(excess), n) "dissociation" surface is generated from a series of measurements over the range 0 less than or equal to E(excess) less than or equal to 1.8 eV and displays features attributable to attractive forces at small E(excess) and repulsive interactions at high E(excess). This phi(E(excess), n) surface is essentially independent of cluster size in the range 18 less than or equal to n less than or equal to 33, where all clusters are characterized by a single phi(E(excess)) curve. Similarly, phi(E(excess), n) becomes independent of E(excess) at high E(excess) (greater than or equal to 1 eV) with a characteristic phi(n) dependence. At both large E(excess) and large n, phi(E(excess) n) displays a plateau at about 0.70 which is very weakly dependent on both E(excess) and n. We interpret the shape of the surface in the context of a model recently developed by Apkarian and co-workers (J. Phys. Chem. 1994, 98, 7966) to explain the excess energy-dependent dissociation yields for small molecules in rare-gas matrices.