Fifty-two gigawatts (about 16% of the existing coal fleet) of coal-fired electric generating capacity has been announced for retirement by 2025. Of this, about 45 GW will retire by 2016. Coal-fired units slated for possible retirement, for the most part, are small in size, lack environmental controls, and are over 50 years old. Most also do not have the capability to burn sub-bituminous coal, a cheaper and low-sulfur coal type mined mostly in Powder River Basin, Wyoming. Retirement announcements have accelerated since 2010 when natural gas prices fell below $3/MMBtu, marking a nearly 80% decrease from just two years earlier. The Environmental Protection Agency also finalized the Mercury and Toxics Standards (MATS) rule in 2011. The rule would regulate the emissions of particulate matter, mercury, and acid gases from coal plants. Announced coal plant retirements are concentrated in the Midwestern and Southeastern regions of the country. Together, these two regions account for 38 GW, or about three-quarters of all announced retirements.