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Air-fuel ratio cylinder imbalance is a condition where the air-fuel ratio in one or more cylinders is different than the other cylinders. When air-fuel ratio cylinder imbalance occurs in one or more cylinders the fuel delivery system is unable to maintain a proper vehicle emission level. It is required for on-board diagnostics to detect air-fuel ratio cylinder imbalance levels which cause the fuel delivery system to be unable to maintain vehicle emissions at or below 1.5 times of any of the applicable FTP (Federal Test Procedure) emission standards. Currently California Air Resources Board (CARB) only requires on-board diagnostics to detect exhaust bank specific air-fuel ratio cylinder imbalance. In the near future CARB will require on-board diagnostics to detect cylinder specific air-fuel ratio cylinder imbalance. This paper presents a non-intrusive approach on determining single cylinder air-fuel ratio imbalance identification (ID) with an oxygen sensor.