Major energy sources and percent share of total U.S. electricity generation in 2015 (data as of April 1 2016):
Coal = 33%
Natural gas = 33%
Nuclear = 20%
Hydropower = 6%
Other renewables = 7%
(Biomass = 1.6%)
(Geothermal = 0.4%)
(Solar = 0.6%)
(Wind = 4.7%)
Petroleum = 1%
Other gases = <1%
Source: http://www.eia.gov/tools/faqs/faq.cfm?id=427&t=3