Preparing a compliance plan to meet the requirements of the United States Environmental Protection Agency’s (EPA) Clean Power Plan (CPP) can be daunting due to the wide spectrum of compliance options available to states. Nonetheless, energy efficiency has the potential in many states to play a pivotal role in meeting greenhouse gas reduction requirements at least cost. At a market transformation conference held by the American Council for an Energy-Efficient Economy (ACEEE), Christopher James underscored the important part air regulators can play in implementing energy efficiency, and described methods for accurately quantifying the savings from efficiency measures. The “mobile source analogy” offers an innovative approach to quantifying the emissions avoided by energy efficiency programs by drawing parallels from measuring emissions from motor vehicles. By familiarizing themselves with the intricacies of energy efficiency programs and the associated evaluation, measurement, and verification methods, air regulators can make the most of energy and economic benefits, while establishing reliable replacements for retiring fossil fuel plants.