A novel approach for monitoring oil-water interface level and oil level in a single tank is presented. A liquid level sensor has been developed that is suitable to determine the oil-water interface level and oil level. This sensor can realize two sensing functions, namely, inductive and capacitive sensing functions. For achieving this multi-sensing function, the designed sensor employed two coils wound on a plastic pipe. According to the relationships between oil-water interface level and inductance produced by a coil connected using the two coils, oil level and capacitance measured from two coils, the oil-water interface level and the oil level can be estimated at same time.