What is the largest fuel source for electricity in the United States?

Coal. It accounted for 44% of electricity generation in 2009. However, Coal’s share of electricity generation in the United States has decreased 8% since 1990. Why?

The United States has decreased its use of coal as a result of increased environmental regulations and a shift toward greater utilization of natural gas as a base load energy source. Natural gas has grown as a source of energy due to its greater viability as a local energy source due to technological advances that have made accessing difficult deposits economically viable. These advances are not without peril, recent analysis of natural gas extraction have suggested that possible downsides include possible drinking water contamination from hydrological fracturing or “fracking” activities and methane emissions comparable to coal production.   

Figure 1 shows us the current (2009) status of electricity generation in the US.

2009 Electrical Generation by Source

Petroleum, as a source of electricity, has diminished significantly to less than 1% in 2009. Most petroleum is used for transportation and industrial purposes.

What can I do to reduce the impact of energy use on the environment?
The US Department of Energy provides a list of websites and resources here to help consumers who are interested in purchasing renewable energy. Approximately 50% of US consumers have access to alternative sources of energy through their current power company. Green energy does cost a little more upfront, but the benefits from lower air pollution, fewer emissions, and a lower demand for foreign energy imports are worthy of considerations when purchasing your energy.