This report reviews six recent studies (from 2002 through 2006) by states and utilities to assess the energy saving potential in existing commercial buildings. The studies cover all or portions of California, Connecticut, Vermont, Colorado, Illinois, and the Pacific Northwest. The studies clearly reveal that lighting remains the single largest and most cost effective end use that can be reduced to save energy. Overall the study indicated that with existing technologies and costs, a reasonable range of economic savings potential in existing commercial buildings is between 10 and 20 percent of current energy use. While not a focus of the study, an additional conclusion is that implementation of commercial building monitoring and controls would also play an important role in the nations efforts to improve energy efficiency of existing buildings.