Described here is a semiquantitative theoretical treatment of the kinetics of outer sphere electrochemical reactions. The framework presented here, which is based on simple physical arguments, predicts heterogeneous rate constants consistent with previous experimental observations (k(0) > 10 cm/s). This theory is applied to the analysis of voltammetry experiments involving ultramicroelectrodes modified with thin, insulating oxide films where electronic tunneling between the electrode and redox species in solution (metal-insulator-solution tunneling) is expected to play a prominent role. It is shown that analysis of the voltammetric response of an outer sphere redox couple can be used to track changes in the structure of the adsorbed insulating layer.