Some important characteristics of the amperometric oxygen sensor are examined in detail with particular emphasis on the influence of electrode polarization on sensor behavior. First, we briefly discuss the theoretical framework describing the operation of the amperometric sensor and then describe operational characteristics and observations of anomalous behavior in light of that framework. For the experimental work, a double-cell configuration with a drilled cover was used; the second cell served both as the diffusion barrier and as a potentiometric sensor for monitoring the oxygen partial pressure inside the cavity. It was found that the oxygen partial pressure varied significantly from the cavity entrance to the pumping cell cathode surface. Oxygen depletion inside the cavity strongly influenced the cathode polarization and sensor behavior. Upon application of increasing applied voltage, the maximum pumping capacity of the cathode decreased with oxygen depletion until it became equal to the diffusion limited current enforced by the diffusion barrier. Upon application of even higher voltages, oxygen could not be further depleted at the cathode surface; no further changes in the system occurred until the onset of electronic conduction in the cell electrolyte, where the current increased once again. Electronic conduction was shown to be the cause of anomalous behavior for the sensor where higher current was observed for lower oxygen concentration. A linear response for the amperometric sensor was realized only for oxygen concentrations in the range 0.1 to 25%.