Difference Between Leaded Petrol and Unleaded Petrol

Petrol is a petroleum product. It is created by a technique known as fractional distillation. Petroleum is used to make kerosene and other polymeric goods in addition to gasoline. Petrol is an important fuel in the vehicle industry. The terms leaded petrol and unleaded petrol is universally recognizable for individuals who travel.

When petroleum mixture, often known as gasoline, gas, or petrol, is used in cars or other vehicles, it enters the combustion engine and is rapidly compressed. Because of this compression, it tends to explode on its own or auto-ignite, causing engine damage. This is referred to as knocking. This prompted more investigation, resulting in leaded chemicals added to gasoline to avoid engine damage. The fuel is known as leaded petrol. Before adding lead compounds to gasoline, it was pure gasoline, unleaded gasoline.

Petroleum firms began adding lead to gasoline, and this technique spread around the world. Leaded gasoline enabled automobile makers to experiment with engines, resulting in more powerful, higher compression engines with no concern of petrol knocking the engine. Environmentalists voiced concerns about lead being added to gasoline in the 1980s, causing the technique to fade.

Lead is a hazardous chemical, often known as heavy metal, with serious consequences for human health and the environment. Since the mid-1970s, when all automobile manufacturers switched to catalytic converters in new vehicles, leaded gasoline usage has declined since it was discovered that leaded gasoline was incompatible with catalytic converters. The practice was also shaken when the government imposed differing taxes on leaded and unleaded gasoline.

Leaded gasoline has progressively been phased out in practically all world countries. To reduce engine knocking, other additives such as hydrocarbons, ethers, and alcohol are employed in place of lead compounds.

Almost every country in the world, aware of the negative effects of lead on health and the environment, is developing plans to phase out leaded gasoline. At the pump, many types of petrol are available. Although some are self-explanatory, others, such as leaded and unleaded petrol, can be perplexing.

The ingredient tetraethyl lead is the major difference between leaded and unleaded petrol. Other varieties have been used, but this is the most common. This lead-containing ingredient is used in leaded gasoline but not in regular petrol.

Read this article to find out more about Leaded Petrol and Unleaded Petrol and how they are different from each other.

What is Leaded Petrol?

The chemical formula for leaded petrol is tetraethyl lead or TEL. It's a lead-organolead complex. Leaded petrol reduced engine knocking and gained popularity due to its antiknock efficacy. Because of the peculiar properties of leaded petrol, it was a cheap yet effective fuel. The stench of leaded petrol is sweet and pleasant. Leaded petrol offers many advantages, but it also has many problems.

Leaded petrol emits lead into the atmosphere, which is toxic to people and animals. Leaded petrol has lead additives, whereas unleaded petrol contains aromatic additives. Leaded petrol is prohibited, although unleaded gasoline is widely used by the general public worldwide.

Lead is discharged into the air during the combustion of leaded petrol. Lead is a significant polluter that harms not just the environment but also those who are exposed to it. The widespread use of leaded gasoline caused a continuous rise in the lead levels of persons living in densely populated regions where automobiles were common. Prolonged exposure to high levels of lead can result in lead poisoning, which can be lethal.

What is Unleaded Petrol?

Unleaded petrol is a fuel that does not contain or emit any lead compounds. The majority of automobiles operate on unleaded gasoline. Unleaded petrol is a very explosive and volatile hydrocarbon combination. Hydrocarbons' primary elements include heptane, hexane, octane, and others. Most current internal combustion engines run on unleaded petrol.

Regular gas is another name for unleaded petrol. It was offered as a replacement for leaded gas since leaded gas produced and emitted hazardous and poisonous chemicals. People were discouraged from using leaded petrol; later, different tax rates were established to prevent the general public from using leaded petrol.

As the dangers of lead were revealed, governments were eager to phase out leaded petrol. They began with differing tax rates for leaded and unleaded petrol, and several finally banned leaded petrol, imposing extremely harsh fines on individuals caught carrying or using it.

Petrol was merely petrol until engines began to have greater compression rates and began to auto-ignite, a phenomenon known as knocking or pinging. Petrol producers realized that adding a lead-based additive reduced the banging, resulting in leaded gasoline. After it was known that lead had certain negative side effects, governments began to restrict leaded gasoline and encouraged firms to create unleaded gasoline as an alternative.

Differences between Leaded Petrol and Unleaded Petrol

The following table highlights the major differences between Leaded Petrol and Unleaded Petrol −


Leaded Petrol

Unleaded Petrol


Leaded petrol mainly consists of tetraethyl lead

Unleaded petrol includes benzene, naphthalene, trimethylbenzene, MTBB, and others.

Currently in use

Leaded petrol is not popular and it is currently not used by anyone

Unleaded petrol is currently in use.


It emits heavy metals such as lead as well as other hazardous gases.

It emits harmful gases such as carbon monoxide, carbon dioxide, and others.


It is affordable, can eliminate engine knocking, and can raise the engine's octane rating.

It does not emit any dangerous heavy metals, such as lead, and poses no major health dangers.


Heavy elements such as lead, which are released during the combustion of leaded gasoline, can be lethal to humans.

It is costly and pollutes the environment owing to the aromatic additions.


Leaded petrol is dangerous to people and animals, but unleaded petrol poses no severe health risks to humans. Leaded petrol emits toxic gases and heavy metals, causing pollution, whereas unleaded petrol emits no major harmful gases. Leaded petrol emits lead into the air, which can cause lead poisoning, whereas unleaded petrol emits no lead into the air.

Leaded gasoline includes lead additives, whereas unleaded gasoline does not. Leaded gasoline emits more pollutants than unleaded gasoline. Leaded gasoline is more hazardous to one's health than unleaded gasoline. Unleaded gasoline is accessible for public use. However, leaded gasoline is prohibited.

Updated on: 13-Feb-2023

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