A simple resistance-based exhaust gas sensor has been developed for use in closed loop engine control systems. The active element is a highly porous thick film of low impurity content titania. These sensors provide good air-fuel ratio control near the stoichiometric value in feedback operation for a fixed series resistance over a wide exhaust gas temperature range. Electrical heating or temperature compensation are not needed over the full operating range. Sensor transient response in closed loop operation is faster than that of an electrically heated zirconia sensor. Two types of titania thick film sensors maintained air-fuel ratio near stoichiometry over 80 000 km (50 000 mi) simulated durability exposure.