A zirconia-based oxygen sensor was studied after long exposure to the atmosphere of an industrial glass-making furnace. The study included X-ray diffraction, scanning electron microscopy/EDS, and impedance spectroscopy measurements performed on electroded sections of the sensor tube, along the entire sensor length. The final goal was the identification of the causes for sensor failure and possible correlation between the results obtained from different destructive and nondestructive techniques. Data obtained was used to demonstrate that the sensor degradation could be evaluated from constant frequency measurements. The range of allowed frequencies (temperature dependent) to be used for such characterization is identified in this work.