When oil comes out of the ground, it doesn't magically transform itself into gasoline or home heating oil. Oil refineries must convert crude oil into useable products. There are 153 of these refineries in the United States and more than 90 million people live within 30 miles (48.28 kilometers) of them. Yet each year, these refineries release millions of pounds of cancer-causing chemicals, including benzene, butadiene and formaldehyde into the environment. In addition, the refineries spew nickel, lead, sulfur dioxide, and other pollutants that can cause heart disease, asthma and other health problems [source: Brune].
For the most part, biofuel refineries, which turn feedstock such as corn and soybean into biofuel, are more environmentally friendly. For example, ethanol plants fueled by natural gas emit very few pollutants, including greenhouse gases. However, coal-fired ethanol plants release copious amounts of carbon and other greenhouse gases -- not to mention a significant amount of particulate matter -- into the atmosphere. On the other hand, ethanol plants fueled by biomass and biogas produce less gas emissions and are cleaner to run [source: Oregon Environmental Council].