Abstract: A method and apparatus for measuring quality of cooking or frying oil in situ is provided. The oil quality sensor apparatus utilizes simultaneous monitoring of change in the capacitance and optical transmission of the oil in situ in the cooking or frying temperature range. The sensor monitors the chemical degradation as well as the sensory acceptance of the oil. A large, high surface area and multi-plated parallel plate capacitor is used to measure the capacitance to provide a reliable measure of concentration of total polar materials in the high polar region. A diode laser operating at a wavelength of 675 nm and photodetector are used to measure transmittance of the oil in situ with a microprocessor processing the transmittance and capacitance data. The sensor is programmed to indicate oil is to be replaced if either a preset minimum safe percent transmittance threshold is exceeded based on the transmission measurement or a change in capacitance exceeds a preset threshold value.