Separation of two immiscible liquids by a decanter is an important unit operation widely used in petrochemical processes. However, fluctuations in the feed stream create a difficulty in achieving the desired product by such a unit due to the limitations of interface detection and entrainment of heavy phase into a light phase. This research proposes techniques for estimating and controlling the interface position. The interface position is calculated by using information from an ultrasonic sensor and a pressure transducer. An input/output linearizing controller is applied to control the interface position and total liquid height by adjusting the outflows of each liquid phase. A real-time estimator predicts the feed fraction that cannot be measured directly. The proposed method is evaluated through servo and regulatory tests with a bench-scale palm-oil/water decanter. The experimental results show that the developed method forces outputs to desired setpoints effectively despite the presence of feed disturbances. (C) 2017 Elsevier Ltd. All rights reserved.