Err... natural gas (the largest component of current U.S. power generation) is produced by the exact same big oil companies, for the most part. The three largest natural gas producers in the United States are ExxonMobil, BP, and ConocoPhillips.
Also, before the Arab Oil Embargo hit in 1973 (causing oil prices to skyrocket) a significant amount (though not a majority by any means) of the U.S. electric grid was oil-fired.
Also, before the Arab Oil Embargo hit in 1973 (causing oil prices to skyrocket) a significant amount (though not a majority by any means) of the U.S. electric grid was oil-fired.