The energy performances of 20 commercial buildings, covering the common types found in Hong Kong, have been studied. The monthly electricity billing data as well as the results from computer modeling were analyzed. Energy signatures for the commercial buildings were found by a method similar to PRISM, Correlation equations of energy use with building envelope parameters, such as OTTV, building size, envelope heat gain, and the annual chiller-load were derived. The results are useful for building envelope design. energy audit, and legislative control of energy use in commercial buildings.