An experimental analysis was performed on the transient switching behavior of ZrO2 exhaust gas oxygen sensors. Sensor response delay time and voltage switching rate were investigated as a function of temperature and air-fuel ratio. A theoretical study was first conducted from which mathematical equations were derived describing the delay time and switching rate. Extensive experimental testing was then carried out using a program-controlled functional tester. Sensors of three different forms were tested at temperatures ranging from 780°C down to 170°C with nine different air-fuel ratio excursions across stoichiometry. Test data were further analyzed and the theoretical equations verified.