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Gasoline—a petroleum product

Gasoline is a fuel made from crude oil and other petroleum liquids. Gasoline is mainly used as an engine fuel in vehicles. Refineries in the United States produce about 19 gallons of gasoline from every 42-gallon barrel of crude oil that is refined. Refineries and companies that produce the finished motor gasoline sold in retail gasoline fueling stations may add various liquids so that the gasoline burns cleaner and meets air pollution control standards and requirements. Most of the motor gasoline now sold in the United States also contains about 10% fuel ethanol by volume. This is required by a federal law intended to reduce the amount of oil that the United States imports from other countries.

A gasoline pump showing different grades of gasoline
Many cars on the road

Source: Stock photography (copyrighted)

There are three main grades of gasoline sold at retail gasoline refueling stations:

  • Regular
  • Midgrade
  • Premium

Some companies have different names for these grades of gasoline, like unleaded, super, or super premium, but they all indicate the octane rating, which reflects the anti-knock properties of gasoline. Higher ratings result in higher prices.

Before 1996, lead was added to gasoline as a lubricant to reduce wear on engine valves. Leaded gasoline was banned for sale in the United States on December 31, 1995. Manufacturers recommend the grade of gasoline for use in each model of a vehicle. However, most gasoline-fueled vehicles will operate on regular gasoline, which is usually the least expensive grade.

Last reviewed: August 12, 2016

Gasoline varies by grade and formulation

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Gasoline changes with the seasons.

The main difference between winter- and summer-grade gasoline is vapor pressure. Gasoline vapor pressure is important for an automobile engine to work properly. During winter months, vapor pressure must be high enough for the engine to start easily.

Gasoline evaporates more easily in warm weather, releasing more volatile organic compounds that contribute to health problems and to the formation of ground-level ozone and smog. To cut down on pollution, the U.S. Environmental Protection Agency requires petroleum refiners to reduce the vapor pressure of gasoline during summer months.

In addition to the different grades of motor gasoline, the formulation of gasoline may differ depending on the location or the season. Federal and state air pollution control programs that aim to reduce carbon monoxide, smog, and air toxins require oxygenated, reformulated, and low-volatility gasoline. Some areas of the country are required to use specially formulated gasoline to reduce certain emissions, and the formulation may change during winter and summer months. These area-specific requirements mean that gasoline is not a homogenous product nationwide. Gasoline produced for sale in one area of the United States may not be authorized for sale in another area.

The characteristics of the gasoline depend on the type of crude oil that is used and the setup of the refinery where the gasoline is produced. Gasoline characteristics are also affected by other ingredients that may be included in the blend, such as ethanol. Most of the fuel ethanol added to gasoline is made from corn grown in the United States.

Last reviewed: September 2, 2016