On 29 June 2012, the Illinois Commerce Commission (ICC) announced the Alternative Compliance Payment (ACP) rates for the Renewable Portfolio Standard (RPS) compliance year ending 31 May 2012. The state's alternative retail energy suppliers (ARES) are required to fulfill at least half of their RPS obligation with ACPs paid into the Renewable Energy Resource Fund (RERF) for purchase of additional RECs on the ARES' behalf. The rates are US$0.95 and US$0.97/MWh of RPS obligation for ARES in the territories of the state's incumbent investor-owned utilities (IOUs), Commonwealth Edison (ComEd) and Ameren Illinois (Ameren), respectively.