Fuel oil pollution control and additional maintenance required after burning it often outweigh the low cost of the fuel. Burning fuel oil, particularly residual fuel oil, produces uniformly higher carbon dioxide emissions than natural gas. Heavy fuel oils continue to be used in the boiler "lighting up" facility in many coal-fired power plants. This use is approximately analogous to using kindling to start a fire. Without performing this act it is difficult to begin the large-scale combustion process. The chief drawback to residual fuel oil is its high initial viscosity, particularly in the case of No. 6 oil, which requires a correctly
Ethanol fuel by country and Hawaii — require ethanol to be blended with gasoline motor fuel. Many cities also require ethanol blends due to non-attainment of federal air quality goals. Several motor vehicle manufacturers, including Ford, Chrysler, and GM, sell flexible-fuel vehicles that can use gasoline and ethanol blends ranging from pure gasoline all the way up to 85% ethanol (E85). As of early 2013, there were about 11 million E85-compatible vehicles on U.S. roads, though actual use of E85 fuel is limited, not only because the ethanol fueling infrastructures is limited, but also because many owners are not aware their vehicle is flex-fuel