About what percentage of energy used in the United States comes from fossil fuels?
From the official source:
In 2015, fossil fuels made up 81.5% of total U.S. energy consumption, the lowest fossil fuel share in the past century.
for all of your USA energy data.
Three fossil fuels—petroleum, natural gas, and coal—have provided more than 80% of total U.S. energy consumption for more than 100 years.