Gasoline—a petroleum product
Gasoline is a fuel made from crude oil and other petroleum liquids. Gasoline is mainly used in vehicle engines. Petroleum refineries and blending facilities produce finished motor gasoline for retail sale at gasoline fueling stations.
Petroleum refineries mostly produce gasoline blending components called gasoline blendstocks, which require blending with other liquids to make finished motor gasoline. Most finished motor gasoline is produced at blending terminals, where gasoline blendstocks, finished gasoline, and fuel ethanol are blended to produce finished motor gasoline in different grades and formulations. Some companies also have detergents and other additives blended with their gasoline before delivery to their retail outlets. Blending terminals are more numerous and widely dispersed than petroleum refineries, and they have equipment for filling tanker trucks that transport finished motor gasoline to retail outlets.
Most of the finished motor gasoline now sold in the United States contains about 10% fuel ethanol by volume. Ethanol is added to gasoline mainly to meet the requirements of the Renewable Fuel Standard, which is intended to reduce greenhouse gas emissions and the amount of oil that the United States imports from other countries.
Gasoline varies by grade
Three main grades of gasoline are sold at retail gasoline refueling stations:
Some companies have different names for these grades of gasoline, such as regular, unleaded, mid-grade, medium, super, premium, or super premium, but they all indicate the octane rating, which is the antiknock property of gasoline. (No grade of motor gasoline now sold in the U.S. contains lead.) The lowest octane rating gasoline is usually the least expensive. Vehicle manufacturers recommend the grade of gasoline for use in each model of their vehicles.
A gasoline pump showing different grades of gasoline
Source: Stock photography (copyrighted)
Gasoline also varies by formulation
In addition to the grade of motor gasoline, the formulation of gasoline may differ, depending on the location where it is sold or the season of the year. 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 the same everywhere. Gasoline produced for sale in one area of the United States might not be authorized for sale in another area.
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. In the summer, a lower vapor pressure is required in many areas to reduce air pollution.
Gasoline evaporates more easily in warm weather, releasing more volatile organic compounds that contribute to health problems and to 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 the summer.
The characteristics of gasoline depend on the type of crude oil used to produce it and the setup of the refinery that produces it. Gasoline characteristics are also affected by other ingredients that may be included in the blend, such as ethanol.
Last updated: December 28, 2022