Powder River Basin (PRB) coal has given coal-fired plants an environmentally conscious, inexpensive alternative to traditional bituminous coal since the 1980s. The lower NOx and SO2 in PRB coal reduced power plant emissions, decreasing pollution, and appeasing the 1990 Clean Air Act. At the same time, the low cost and availability made PRB coal not only a viable option, but a fuel of choice. While PRB coal was the predominant emission efficient energy source in 1990, in 2012, it no longer reins as the most environmentally friendly fuel. With the current government crack-down on coal-fired power plants, the existing plants will likely be the last.