The paper presents the study on operation and performance of thermal energy storage (TES) system. The TES system is installed at a cogeneration plant for campus cooling. Operating data from 2006 until 2009 were anlaysed to evaluate the operating modes, half-cycle figure of merit (FOM) and thermocline performance of the TES system. The findings indicate that the TES system was operated based on partial mode strategy. The average half-cycle FOM evaluated for charging and discharging are 0.47 and 0.67 respectively. The thermocline thickness estimated is 1.5 m. The temperature distribution profiles indicate that the TES functioned as stratified TES. © 2011 Published by Elsevier Ltd.