The overall exergy losses of co-production systems were decomposed into five sub-systems: chemical reaction processes, heat exchange processes, external exergy losses, turbine/mechanical exergy losses and others. By defining new parameters called energy-saving factors, we quantitatively describe the contribution of these processes to the overall energy savings relative to separate production systems. A methanol/electricity co-production system is taken as case study, results show that heat exchange processes are the main contribution to the energy savings. (C) 2009 Elsevier Ltd. All rights reserved.