Midwest Independent Transmission System Operator (MISO) is a nonprofit member-based organization regulated by the Federal Energy Regulatory Commission (FERC). As a Regional Transmission Organization (RTO), MISO provides electricity consumers in 13 states with regional grid management and open access to transmission facilities at a tariff closely regulated by FERC. MISO follows a cycle known as the MISO Transmission Expansion Plan (MTEP) that results in annual recommendations to proceed with expansion projects, subject to approval by the independent MISO board of directors. The Energy Storage Study—a targeted study carried out during the 2011 MTEP cycle—models several hypotheses surrounding pumped hydro storage (PHS), compressed air energy storage (CAES), and battery storage technologies and their impact on the MISO footprint. The study specifically explores reliability, market, and planning benefits that storage technologies could provide as well as the economic potential for storage technologies in MISO.