As power systems integrate more intermittent renewable generation, and as extreme weather events become more frequent with climate change, power systems are likely to require increasing amounts of spinning reserves in order to maintain reliable operation. While traditionally spinning reserves have been supplied by generators, demand-side resources can also provide reserves by increasing or decreasing consumption in response to system needs. As a major contributor to peak system loads, air conditioning equipment is a promising source of demand-side spinning reserves. Through building energy modeling and simulation, this paper demonstrates, for the first time, the technical feasibility of providing spinning reserves by curtailing air conditioning systems in commercial buildings, while maintaining occupant comfort by providing cooling from thermal storage. The economic benefits to the building owner are shown to be attractive, primarily due to capacity payments in the spinning reserves market. Furthermore, it is possible for a building equipped with thermal storage to participate in both frequency regulation and spinning reserves markets for more economic benefits as spinning reserves are less frequently deployed. (C) 2015 Elsevier B.V. All rights reserved.