A method of measuring oxygen partial pressure in gases, such as hot engine exhaust gases, uses a calibrated luminescence sensor and comprises the steps of bringing nanocrystalline zirconium dioxide ZrO2 (2) in said sensor into contact with a gas to be measured, illuminating the zirconium dioxide with a UV-VIS light pulse emitted from a light source (3) and adapted to induce luminescence of the zirconium dioxide, registering the time dependence of the luminescence intensity of the ZrO2 using a photodetector (4) and a recorder (5), determining a particular intensity, e.g., the maximum intensity of the registered luminescence pulse, and comparing said determined intensity with calibration data of the luminescence intensity as a function of oxygen partial pressure for the sensor temperature at the time of the measurement.