Gasoline
U.S.

From 1998 to 2004, the price of gasoline fluctuated between $0.26 and $0.53 per liter ($1 and $2/U.S. gal). After 2004, the price increased until the average gasoline price reached a high of $1.09 per liter ($4.11/U.S. gal) in mid-2008 but receded to approximately $0.69 per liter ($2.60/U.S. gal) by September 2009. The U.S. experienced an upswing in gasoline prices through 2011, and, by 1 March 2012, the national average was $0.99 per liter ($3.74/U.S. gal). California prices are higher because the California government mandates unique California gasoline formulas and taxes.

In the U.S., most consumer goods bear pre-tax prices, but gasoline prices are posted with taxes included. Taxes are added by federal, state, and local governments. As of 2009, the federal tax was $0.049 per liter ($0.184/U.S. gal) for gasoline and $0.064 per liter ($0.244/U.S. gal) for diesel (excluding red diesel).

About nine percent of all gasoline sold in the U.S. in May 2009 was premium grade, according to the Energy Information Administration. Consumer Reports magazine says, "If says to use regular fuel, do so—there's no advantage to a higher grade." The Associated Press said premium gas—which has a higher octane rating and costs more per gallon than regular unleaded—should be used only if the manufacturer says it is "required". Cars with turbocharged engines and high compression ratios often specify premium gasoline because higher octane fuels reduce the incidence of "knock", or fuel pre-detonation. The price of gasoline varies considerably between the summer and winter months.

There is a considerable difference between summer oil and winter oil in gasoline vapor pressure (Reid Vapor Pressure, RVP), which is a measure of how easily the fuel evaporates at a given temperature. The higher the gasoline volatility (the higher the RVP), the easier it is to evaporate. The conversion between the two fuels occurs twice a year, once in autumn (winter mix) and the other in spring (summer mix). The winter blended fuel has a higher RVP because the fuel must be able to evaporate at a low temperature for the engine to run normally. If the RVP is too low on a cold day, the vehicle will be difficult to start; however, the summer blended gasoline has a lower RVP. It prevents excessive evaporation when the outdoor temperature rises, reduces ozone emissions, and reduces smog levels. At the same time, vapor lock is less likely to occur in hot weather.
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