Solar power plants that are based on an array of parallel parabolic trough solar collectors currently use oil as the heated fluid. Direct steam generation (DSG) has the potential of being a more efficient and less costly process owing to the elimination of oil as an indirect secondary heating medium and the elimination of heat exchanges and extra equipment needed for the transfer of heat from oil to water/steam. Unfortunately the use of DSG may possess problems regarding undesired flow distribution among the parallel pipes as well as possible flow instabilities. In this work we propose a control procedure that can adjust the flow rate in each of the parallel pipes to a desired quality at the pipes exit. (c) 2007 Elsevier Ltd. All rights reserved.