This paper describes the analysis of a real case of multiple Aquifer Thermal Energy Storage systems. The Hague, the capital city of the province of South Holland in the Netherlands, is densely populated with many ATES systems. A total of 19 ATES systems are installed in an area of 3.8 km(2) with a total of 76 functioning wells. The analysis focuses on the development of a coupled groundwater flow and heat transfer model over a period of 10 years. Results are then post-processed to evaluate efficiency of each individual well and system. Efficiency of the ATES systems has ranged between 68% and 87%. The analysis showed that efficiency tends, in general, to increase over time and stabilize at an asymptotic value after few years. Analysis of interference among individual wells of an ATES system and wells of other systems showed that interference could, in fact, have a positive impact on the efficiency of a well/system. Interference can increase efficiency of an ATES system since it can help in trapping energy (cold or warm) within the capture zone of all operating ATES systems. In the study area, the interference phenomenon affects efficiency, in general, positively where it increases the efficiency of individually operating wells by a maximum of 20%. However, the phenomenon also affects efficiency of some wells negatively where it reduces the efficiency of individually operating wells by a maximum of 25%. In average, systems in the study area are positively affected by interferences among each other with an overall average of 3.2% for all wells (over the 10 years operation period). (C) 2013 Elsevier Ltd. All rights reserved.