This paper presents several examples showing the manner in which metered energy consumption data in an existing building can be employed to determine how much energy is used for each major purpose and when that energy is used. Buildings used as examples are a high-rise apartment house, a hotel, and an office building. By knowing how much energy is used for each purpose in a building, it is possible to identify and prioritize the most cost-effective means for reducing energy consumption and make comparisons among similar buildings and functions in order to identify unique or unusual situations.