Unleaded gas refers to gasoline processed without tetraethyl lead. Most gas vehicles have a spark-ignited combustion engine. Fuel enters the combustion chamber, mixes with air, and then ignites with a spark from the spark plug.1 The combustion gas expands to push the piston, rotate the crankshaft, and move the gears to move the vehicle.2
Leaded gasoline burned through the engine can contaminate the environment and impact people with lead exposure. By the mid-1980s, unleaded gasoline was the standard fuel for passenger cars, and the Clean Air Act finally banned the sale of all leaded gas in the U.S. in 1996.3 U.S. gas stations sell only diesel and unleaded gasoline.
Here’s what you should know about unleaded gasoline.
With the exception of diesel fuel, all gasoline sold at gas stations is some form of unleaded gas. The different unleaded fuel options you see at a gas station include regular, mid-grade, and premium gas, all of which have different octane levels.
The octane rating of different fuel types measures fuel stability, and fuel grades with higher octane ratings have greater fuel stability. Both spontaneous and controlled explosions occur in an engine, but spontaneous combustion creates pressure that can disrupt and damage engines.
Octane ratings measure the fuel’s ability to resist or reduce this spontaneous combustion damage — often referred to as “engine knocking.” Although newer-model cars have features to prevent engine knocking, higher octane fuel may also improve engine performance and fuel efficiency and reduce CO2 emissions.
At a gas station, you’ll generally see three separate numbers between 87 and 94 listed on the pumps. These numbers refer to the octane rating of the gasoline. All three of these options are unleaded gasoline, though they fall into different categories as follows.
Created in 1921, lead gasoline was the standard fuel for vehicles before decades of research established how lead gasoline harms the environment and the public. The U.S. Energy Information Administration notes that any gasoline burned, including unleaded, contributes to air pollution and produces carbon dioxide.
The current use of unleaded gas includes pros and cons that affect vehicle performance and the environment.
All vehicle manufacturers either recommend or require the use of an unleaded gasoline with a specific octane level. Choosing the correct gas for your vehicle helps your engine run optimally. Many vehicle engines can run on regular gasoline, but some manufacturers recommend mid-grade or premium gasoline.
Here are a few places you may find your manufacturer’s recommendation:
Owner’s manual: Most manufacturers list this information in the manual.
Gas cap: If your vehicle requires mid-grade or premium fuel, your manufacturer will typically include a sticker with the recommended fuel type inside the fuel door.
Manufacturer website: If you’re not sure which gas type is best for your vehicle, you may find the information on your car manufacturer’s website.
The U.S. Energy Information Administration releases average fuel cost data on its Gasoline and Diesel Fuel Update page. The data displays the cost increase from the previous year and fluctuates from week to week. The prices in most regions of the United States — with the exception of the West Coast — follow a similar pattern week over week and year over year.6
Several factors affect gasoline prices, including the cost of crude oil, taxes, and more. Below, you can learn more about the factors that influence retail gasoline prices the most.7
Crude oil costs: Crude oil costs have the most significant effect on retail gas prices. A number of factors influence crude oil prices. These include Organization of the Petroleum Exporting Countries (OPEC) and non-OPEC fuel supplies and Organization of Economic Cooperation and Development (OECD) and non-OECD fuel demand. Financial markets, spot prices, and the balance between supply and demand can also affect costs.
Refining costs and profits: These factors vary by season and by region, as different refineries use different types of crude oil and processing technology to produce gasoline that meets the reduced air pollution requirements in different areas of the country.
Distribution and marketing costs and profits: Local fuel stations may adjust prices based on their individual marketing strategies. Distribution to each retail outlet also affects prices, as some gas station businesses own refineries, while others are independent businesses that need to purchase gasoline for resale.
Taxes: Various taxes also influence the price at the pump, including federal, excise, state, sales, and local taxes.
Geopolitical factors: Geopolitical events, such as conflicts, sanctions, or trade policies, can disrupt the supply and demand for fuel and affect costs.
Knowing which unleaded gasoline to use can help prevent engine damage. The following information can help answer your remaining questions about unleaded gasoline.
Premium gasoline is a type of unleaded gasoline with a specific octane level labeled between 91 and 94. Vehicle manufacturers list the octane rating for each vehicle in the owner’s manual. While many gasoline-fueled vehicles run on “regular” gasoline with an octane level of 87, some vehicles require a higher-octane fuel, like premium gasoline.
While all gasoline is unleaded, the different categories have varying octane levels. Regular unleaded gasoline has an octane rating of 87, while mid-grade and premium unleaded gasolines have higher octane ratings.
The main benefit of using the correct gasoline in your car is to achieve optimal engine performance. Each vehicle manufacturer designs an engine to run on a specific unleaded gasoline octane rating. Octane ratings refer to the ability to resist engine knocking. Using the correct gasoline can help prevent engine damage.
Using gasoline in your vehicle with too low an octane rating can damage your car’s engine and emissions control system. For example, a sports car manufacturer may require or recommend premium gasoline. Using a mid-grade or regular gasoline with lower octane ratings than premium gasoline can result in a higher likelihood of engine knock. Frequent and long-term engine knock can lead to engine damage in older vehicles.
Gas stations typically sell three types of unleaded gas: regular, mid-grade, and premium. Regular has a label of 87, mid-grade will have a label of 89 or 90, and premium unleaded gas has labels ranging between 91 and 94.
Yes. Many vehicles can run on regular unleaded gas, but some need gas with higher levels of octane. If your vehicle needs mid-grade or premium gas, your manufacturer will make a specific recommendation for it. You can typically find the recommendation in your car’s manual and on the gas cap door.
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