A model-based in-/out-flux detection scheme for managed pressure drilling is presented. We apply a globally exponentially stable adaptive observer which estimates the unknown states and parameters of the hydraulic system and in particular quantifies the magnitude of the in-/out-flux and its location in the well. While the observer can be used purely as an in-/out-flux detection system, the paper also presents a simple controller that automatically and effectively stops an in-/out-flux. This novel control scheme departs from common practice for automatic managed pressure drilling, which is to regulate down-hole pressure to some predetermined set point. Experimental results and realistic simulations with a state-of-the-art simulator are provided to show the effectiveness of the method. (c) 2013 Elsevier Ltd. All rights reserved.