The current downward trend in coal - fired generation began in 2007, when increased U.S. production of natural gas (particularly from shale) led to a sustained downward shift in natural gas spot prices and increased generation from natural gas - fired generators. (eia.gov)
Several factors are likely contributing to increased natural gas spot trading in the Marcellus area: (eia.gov)
Key factors likely contributing to increased natural gas spot trading in the Marcellus area include: rapid increases in Marcellus shale gas production; direct deliveries of Wyoming gas to the Ohio / Pennsylvania border through the Rockies Express Pipeline; and increased use of natural gas for power generation. (eia.gov)