This paper focuses on the development of a multi-electrode capacitance probe for interface measurement and phase detection within industrial three-phase separators, used in oil and gas extraction and oil refining processes. The sensors are constructed using printed circuit board (PCB) technology and are embedded within stainless steel casings forming the structure of the probe. The design process was aided by the finite element solutions of the three-dimensional electrostatic problem. A number of solutions were obtained which predict the probe readings for various configurations of phases. Validation of the probe performance was performed using a combination of laboratory and industrial tests in a real scale separator, both with representative process media. A good agreement between the experiments and modelling is shown.