This paper examines the effect of load-sharing operation strategies on the aggregate performance for existing multiple-chiller system under different partial loads and environmental conditions. The various tested load-sharing operation strategies obtain aggregate performance from 1.64 to 2.18 during the day hours and from 1.06 to 1.41 for the full day indicating significant effect of the operation strategies on the aggregate performance. The conventional (same part load ratio) strategies attain aggregate performance that is lower than the best strategy by 22-33%. At very low system partial load, the performance of the multiple-chiller system falls to less than quarter its value at large load whereas the performance of individual chiller drops to about one sixth of its large load value. The load sharing strategy is influenced by many parameters such as the condition of the chillers and compressors, the piping arrangement, and the heat loss from the chilled water piping where these parameters may overwhelm the individual chiller performance. Accordingly, the load-sharing operation strategy may vary from case to another and should be periodically examined to verify proper system operation, rectify the existing chiller performance and identify chiller faults. Therefore, the need for maintenance can be predicted and the standby chiller may be eliminated. (C) 2014 Published by Elsevier Ltd.