The paper presents a novel methodology for the operation of those hydro power plants provided with a single penstock by the optimal distribution of the dispatched power among its available generating units, aiming at the maximum efficiency of the whole power plant energy conversion. While previous optimization methods made use of off-line static curve and parameters or expensive flow meters, the proposed method is on-line in nature and uses a single pressure meter at the end of the power plant penstock. The method was applied to a power plant and has resulted in a higher efficiency operation under several conditions. (C) 2014 Elsevier Ltd. All rights reserved.