The energy efficiency ofmany products has increased markedly over the past decade. A conspicuous exception to this trend is commercialpackaged rooftop air conditioners, which have experiencedlittle to no efficiency improvement since 1992 when the Energy Policy Act of 1992 imposed federal minimum standards. Packaged rooftop units have been estimated to use on the order of76 billion kWh annually in the US, at a cost ofroughly $5.6 billion. Sales of these units are growing, and the majority of units sold have energy efficiency ratios (EERs) at orjust above the current national minimum efficiency standards. In this paper we document the static efficiencies ofcommercialpackaged air conditioners, explore the reasons behindthis efficiency gap, and assess opportunities for overcoming the barriers to efficiency improvements in these products.