Gasoline

Gasoline, also called petrol in some places, is a clear, yellowish liquid that can catch fire easily. It is mainly used as fuel for engines in cars and other vehicles that burn fuel by sparking. This fuel comes from processing crude oil in special factories.

The quality of gasoline is often measured by its ability to prevent early burning inside the engine, which can make the engine work less well. This ability is called the octane rating. In the past, a chemical called tetraethyl lead was added to improve this rating, but it was stopped because it was bad for health. Some special vehicles, like racing cars, still use this kind of fuel.

To make gasoline work better, different chemicals are added. These can help the fuel burn cleaner, stop parts of the engine from rusting, and keep the fuel system clean. Some of these chemicals also contain oxygen, like ethanol, which helps the fuel burn more efficiently.

History and etymology

Main article: History and etymology of gasoline

The word gasoline comes from the word gas, plus special endings called -ole and -ine. In other places, it is called petrol, which comes from an old word for rock oil.

People became interested in fuels like gasoline when they invented engines for cars and other vehicles. In the late 1800s, German inventors made engines called Otto engines. These early engines used a special kind of fuel made from coal gas. As engines improved, scientists found ways to make better fuel from crude oil.

Chemical analysis and production

Gasoline is a special kind of fuel made in oil factories called refineries. It is a mix of different chemicals taken from crude oil. About 19 gallons of gasoline can be made from every 42 gallons of crude oil.

The main parts of gasoline are tiny molecules with 4 to 12 carbon atoms. These come from different processes in the refinery, like distillation and special treatments to change the chemicals. The exact mix depends on the refinery, the type of oil used, and what kind of gasoline is needed. Some important parts include straight-run gasoline, reformate, catalytic cracked gasoline, and others. These are mixed together to make the final gasoline product.

Physical properties

Density

Gasoline has a specific gravity that ranges from 0.71 to 0.77. This means it is lighter than water and will float on top of it. Because it is lighter, water cannot be used to put out a gasoline fire unless it is sprayed in a very fine mist.

Stability

Good gasoline should stay good for about six months if kept in the right way. If stored for longer, it might still work in a car engine but could cause some trouble. To keep gasoline stable, it should be kept in a tight container that does not let air in, and stored in a cool place. If gasoline is not stored well, it can become dirty and hard to use, making it harder to start the engine or causing the car to run badly. Adding a special mixture called a fuel stabilizer can help keep gasoline good for longer. These stabilizers are often used for small engines like those in lawnmowers.

Combustion energy content

When gasoline burns in a car engine, it mixes with air and makes energy, producing carbon dioxide and water as byproducts. Burning gasoline gives off a lot of energy—about 46.7 megajoules for every kilogram. Different types of gasoline can have a little more or less energy depending on how they are made. Some fuels, like liquefied petroleum gas (LPG), have less energy than gasoline by volume but can be more efficient in engines designed for them. This is because they can be compressed more without causing damage inside the engine, allowing the engine to make better use of the energy.

Octane rating

Main article: Octane rating

Octane rating tells us how strong a gasoline is. It is measured compared to a mix of special chemicals. Different places may call this number differently, so the same gasoline might have different numbers depending on where you are.

In places like Finland, Sweden, and Norway, regular gasoline usually has a number of 95, with stronger options at 98. In the United Kingdom, most gasoline sold has a number of 95, with some stronger types at 97 or 98. In the U.S., regular gasoline ranges from 85 to 87, while stronger types go up to 94.

In tall cities like Johannesburg, scientists suggest using slightly weaker gasoline because the air is thinner up high.

Octane ratings became very important for airplanes a long time ago. Stronger gasoline lets airplane engines work harder and make more power.

Additives

See also: List of gasoline additives

Antiknock additives

Tetraethyl lead

Main article: Tetraethyl lead

Gasoline can sometimes cause problems in engines by exploding too early, which can damage the engine. To prevent this, a chemical called tetraethyl lead was added to gasoline in the past. However, we now know this chemical is harmful to health and the environment, and it can damage special parts in cars called catalytic converters. Because of this, rules were made to reduce and eventually stop the use of lead in gasoline.

In the U.S., rules were put in place to lower the amount of lead in gasoline starting in 1973, and by 1996, leaded gasoline was no longer sold for regular cars. Europe also stopped using leaded gasoline by the end of the 1990s. In 2021, the whole world stopped using leaded gasoline, with Algeria being the last country to do so.

Today, other chemicals are used instead of lead to keep engines running smoothly. These include certain types of hydrocarbons, ethers, and alcohols, with ethanol being one of the most common.

Lead replacement petrol

Lead replacement petrol was created for older cars that needed leaded gasoline but couldn’t use unleaded fuel. Instead of lead, it used other metals to protect the car’s engine. It was used in places like the United Kingdom, Australia, and South Africa, but it was later phased out in favor of unleaded gasoline.

MMT

Methylcyclopentadienyl manganese tricarbonyl (MMT) is used in some countries to improve gasoline’s performance. Its use is regulated in many places to make sure it doesn’t harm car emissions systems.

Fuel stabilizers (antioxidants and metal deactivators)

Gasoline can go bad over time if it’s stored for a long period, forming sticky substances that can clog engines. To prevent this, special additives called antioxidants are added to gasoline. These additives help keep the fuel fresh. Another type of additive, called metal deactivators, stops metals in the fuel or engine from causing damage.

Detergents

Gasoline also contains detergents. These help keep engines clean by preventing build-up inside the engine, improving combustion, and helping cars start easily in cold weather. Some gasolines have higher levels of these detergents to keep engines especially clean.

Ethanol

See also: Ethanol fuel and Common ethanol fuel mixtures

European Union

In the EU, it’s common to add a small amount of ethanol—a type of alcohol—to gasoline. Most places allow up to 5 percent ethanol mixed in. Some countries, like Finland, France, and Germany, are discussing allowing even more, up to 10 percent. In Finland, many gas stations sell fuel with 10 percent ethanol.

Brazil

In Brazil, gasoline must contain about 27.5 percent ethanol. Pure ethanol can also be used as fuel.

Australia

Australia uses gasoline with up to 10 percent ethanol (called E10) and up to 85 percent ethanol (called E85). Some states require fuel to contain biofuels, and pumps must clearly show how much ethanol is in the fuel.

U.S.

In the U.S., rules require that a certain amount of ethanol be mixed into gasoline each year. This has caused most gasoline to contain around 10 percent ethanol. Many fuel pumps show a sign saying the fuel may contain up to 10 percent ethanol.

India

India started requiring that gasoline contain 5 percent ethanol in 2007. Now, some places sell gasoline with 10 percent ethanol, and India plans to require even more ethanol in gasoline soon.

Dyes

Main article: Fuel dyes

Gasoline is naturally colorless, but it is often dyed to show what kind of fuel it is. For example, in some places, certain types of gasoline are dyed red or yellow so people know what it’s for.

Oxygenate blending

Oxygenate blending means adding chemicals to gasoline that contain oxygen. This helps reduce harmful gases released from cars. In the U.S., rules once required this to reduce pollution, but these rules have changed. Ethanol is a common oxygenate used around the world, especially in Brazil, where it comes from sugarcane. In the U.S., most ethanol for fuel comes from corn.

Safety

Gasoline is made of many chemicals that can be harmful. It can be dangerous if someone swallows it, breathes in the vapors, or touches it with their skin. It is important to be careful around gasoline and not to play with it or try to use it in ways it was not meant to be used.

Gasoline is very flammable and can catch fire easily. The smoke and gases from burning gasoline can also be harmful to health, causing problems like headaches, dizziness, and more serious issues if a person breathes in too much.

Environmental effect

The air in many big cities has changed from pollution caused by coal to pollution from cars and other vehicles. In the U.S., moving around by car or bus is the biggest reason we release carbon into the air, making up 30 percent of all carbon we send out. When we burn gasoline in cars, it creates carbon dioxide, a gas that helps trap heat in our atmosphere.

Gasoline can also create smog when it mixes with sunlight. Some mixes of gasoline with ethanol (a type of alcohol) can make this problem worse, but changing how much ethanol we use can help. Gasoline can sometimes spill from trucks or storage tanks, which is why many storage places have special tools to catch and stop leaks. Using gasoline can also harm people and the planet in many ways, like making it harder to breathe, hurting crops, and causing extreme weather linked to climate change.

Gasoline can get into soil and water, and people can be exposed to it by breathing it in, eating contaminated water, or having skin contact. Working at a gas station or using machines with gasoline, like lawnmowers, are common ways people come into contact with it.

Use and pricing

In 2021, an energy group said that fuel prices should be set to show their effect on health and the environment.

In Europe, fuel prices are usually higher than in the U.S. because of higher taxes.

From 1998 to 2004, gasoline prices changed between about $1 and $2 per gallon. After 2004, prices went up until they reached about $4 per gallon in mid-2008, then dropped to around $2.60 per gallon by September 2009. Prices rose again by 2011. By March 2012, the national average was about $3.74 per gallon. In California, prices are higher because of special rules and taxes.

In the U.S., gasoline prices include taxes added by federal, state, and local governments. As of 2009, the federal tax was about $0.184 per gallon for gasoline.

Some cars need a special type of fuel with a higher octane rating, which costs more. This is usually needed for cars with turbocharged engines. Gasoline prices change between summer and winter to help with how the fuel evaporates in different temperatures. In winter, the fuel evaporates more easily to help cars start in cold weather. In summer, the fuel evaporates less to help keep the air clean.

Gasoline production by country

Comparison with other fuels

See also: Energy content of biofuel

Below is a table showing how much energy different transportation fuels have compared to gasoline. The table includes information about energy per volume and energy per mass. The data comes from the Oak Ridge National Laboratory's Transportation Energy Data Book.