This paper reviews the concept of peak demand charges on electrical utility bills and provides an analysis of the effect of cool or highly reflective roofs in reducing peak demand charges. The analysis suggests that peak demand charges may account for a significant portion of monthly electric bills across the United States and that cool roofs may provide an equally significant opportunity to reduce these charges when installed on air-conditioned buildings. The analysis also suggests that the peak demand and net energy savings offered by cool roofs are available for both new and existing conditioned buildings in all climates within North America.