The U.S. Department of Energy estimates that 82 percent of the carbon monoxide, 43 percent of the reactive organic gases (precursors to ground level ozone) and 57 percent of the nitrogen oxides in U.S cities are emitted from petroleum-based transportation fuels.

The U.S. Environmental Protection Agency (EPA) says that gasoline is the largest source of manmade carcinogens. The American Lung Association has noted that transportation sources are responsible for 55.8 percent of outdoor air pollution-including 77.3 percent of total carbon monoxide. The South Coast Air Quality Management District in California estimates that mobile sources account for up to 90% of human exposure to Hazardous Air Pollutants (HAPs), or those that cause cancer.

The environmental trend line for oil is getting even worse. For example, all major U.S. oil companies are now invested in extracting oil from tar sands. Tar sand oil extraction uses immense amounts of water, tears up pristine habitats, and can result in up to 300% more greenhouse gas emissions than conventional oil on the production side.

The burning of fossil fuels also contributes to the development of greenhouse gases.