A new concept of misfire detection in spark ignition engines using a wide-range oxygen sensor is introduced. A wide-range oxygen sensor, installed at the confluence point of the exhaust manifold, was adopted to measure the variation in oxygen concentration in case of a misfire. The signals of the wide-range oxygen sensor were characterized over the various engine-operating conditions in order to decide the monitoring parameters for the detection of the misfire and the corresponding faulty cylinder. The effect of the sensor position, the transient response characteristics of the sensor and the cyclic variation in the signal fluctuation were also investigated.Limited response time of a commercially available sensor barely allowed to observe misfire. It was found that a misfiring could be distinguished more clearly from normal combustion through the differentiation of the sensor response signal. The differentiated signal has twin peaks for a single misfiring in a cylinder. Amplitude of the fluctuation of the differentiated signal was used as a monitoring parameter for misfire detection. Transient response was fast enough to detect the misfire even at a high engine speed of 5000rpm. The phase delay angle of the second peak of the differentiated signal from a reference signal was found appropriate for identification of the faulty cylinder. It was confirmed that the phase delay was reliable enough in identifying the misfiring cylinder since the deviation of the cyclic variation in the phase delay in 30∼40 misfiring cycles was small enough.