Leaded Petrol vs Unleaded Petrol: Difference and Comparison

Petrol is a product of petroleum. It is manufactured by a process called fractional distillation. Apart from petrol, petroleum is also used to produce kerosene and other plastic products. Petrol plays a pivotal role as a fuel in the automobile industry.

Petrol is ignited in the engine through a spark plug. There are two types of petrol available – leaded petrol and unleaded petrol.

Key Takeaways

  1. Leaded petrol contains lead additives to boost octane levels, while unleaded petrol does not.
  2. Leaded petrol harms the environment and human health, while unleaded petrol is much cleaner and safer.
  3. Leaded petrol has been phased out in most countries, while unleaded petrol is now the standard fuel used in vehicles.

Leaded Petrol vs Unleaded Petrol

Leaded petrol is a type of petrol which contains tetraethyl lead additives. There are no aromatic additives in leaded petrol. Harmful gasses are released by it. It is not expensive. There are no tetraethyl lead additives in unleaded petrol. It contains 50% of aromatic additives. Toxic gasses are released by it.

Leaded Petrol vs Unleaded Petrol 1

Leaded petrol is an obsolete option for fuel. It is no longer available in the fuel station. Leaded petrol was introduced into gasoline as it could raise the content of octane on the base gasoline. It could reduce the knocking of the engine.

The leaded petrol releases lead as a pollutant in the air. It also releases other harmful gases and causes pollution.

On the other hand, unleaded petrol was introduced as an alternative to leaded petrol. It contains aromatic additives. It is an accepted fuel and is used all over the world. It is more expensive than unleaded petrol.

Comparison Table

Parameters of ComparisonLeaded petrolUnleaded petrol
Constituents Tetraethyl lead Benzene, naphthalene, trimethylbenzene, MTBB, and other compounds
Current usage It is not used currently It is currently used
Emissions It releases heavy metals like lead and other harmful gases It releases toxic gases like carbon monoxide, carbon dioxide, and others
Advantages It is inexpensive, can reduce knocking in the engine, and can increase the engine’s octane rating. It does not release any harmful heavy metals like lead and does not pose serious health risks.
Disadvantages Heavy metals like lead, which are emitted from the combustion of leaded petrol, can be fatal for mankind. It is expensive and causes pollution in the environment due to aromatic additives.

What is Leaded Petrol?

Leaded petrol is tetraethyl lead or TEL. It is an organolead compound. It was used in huge amounts in the 1920s, as it was found to increase the octane rating and allow the compression of the engine to rise substantially.

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Leaded petrol could reduce knocking in the engine and thus gained popularity due to its antiknock effectiveness. The antiknock characteristics were found by research by General Motors.

The unique characteristics of leaded petrol made it an inexpensive yet effective fuel. The leaded petrol has a sweet, pleasant odour. It has a density of 1.653 g per cubic centimetre.

The fuel’s melting point is -136°C while the boiling point is 84 – 85°C. The refractive index of the fuel is 1.5198, and has a structure of tetrahedral with a dipole moment of 0 D.

Leaded petrol has several advantages but numerous disadvantages too. Leaded petrol release leads into the air, harming humans and animals. The lead released can poison the catalytic converters, and this causes spark plug fouling.

There have been researches conducted on automotive fuel to evaluate its parameters.

From the 1970s, the awareness about leaded petrol grew in number and resulted in a decrease in usage of the same. Eventually, it was banned.

Later, in a study of 2011, it was found that after the ban on leaded petrol, there were 1.2 million fewer deaths. The UNEP (United Nations Environment Programme) has declared an official end to the usage of the same.

What is Unleaded Petrol?

Unleaded petrol refers to a fuel that does not contain or release any lead compounds. Most of the vehicles run on unleaded petrol. Unleaded petrol is a volatile flammable mixture of hydrocarbons.

The main constituents of hydrocarbons are heptane, hexane, octane, and others. Unleaded petrol is the basis of most modern internal combustion engines.

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Unleaded petrol is also known as regular gas. It was introduced as an alternative to leaded gas as leaded gas was producing and emitting harmful and toxic substances.

People were discouraged from using leaded petrol, and later different tax rates were imposed to stop the mass from using leaded petrol.

Eventually, leaded petrol was completely banned and unleaded petrol was used all over the world commercially.

The engines that run on unleaded petrol combine gas and air to compress and then ignite the engine. The ignition is done with a spark. Vehicles with unleaded petrol give moderate to high mileage.

The price of unleaded petrol fluctuates every day. Unleaded petrol does not contain any additive tetraethyl lead.

Unleaded petrol does not cause much harm to the environment and does not release any toxic heavy metals like lead. It does not pose any serious health risk and is widely available and accepted for fuel all over.

Unleaded petrol is also available with 10% bioethanol and is called E10 petrol, which has the least risk to the environment.

Main Differences Between Leaded Petrol and Unleaded Petrol

  1. Leaded petrol consists of lead additives, while unleaded petrol consists of aromatic additives.
  2. Leaded petrol is banned from usage while unleaded petrol is accepted worldwide and consumed as a fuel by the mass.
  3. Leaded petrol is hazardous for humans and animals, while unleaded petrol does not pose any serious health problems to mankind.
  4. Leaded petrol releases harmful gases and heavy metals and causes pollution, while unleaded petrol does not release any major harmful gas comparatively.
  5. Leaded petrol releases lead into the air, which can cause lead poisoning, while unleaded petrol does not release any lead in the air.
  1. https://www.sciencedirect.com/science/article/pii/S0048969705004900
  2. https://www.scielosp.org/article/ssm/content/raw/?resource_ssm_path=/media/assets/bwho/v80n10/8010a02.pdf

Last Updated : 11 June, 2023

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17 thoughts on “Leaded Petrol vs Unleaded Petrol: Difference and Comparison”

  1. This post is a comprehensive resource of knowledge about leaded and unleaded petrol. It’s incredible to see the stark differences in how they affect us and our environment.

  2. I’m glad we moved away from leaded petrol, it was causing so much harm. This is a great description of the differences and the history behind them, which brings even more understanding to the topic.

  3. The historical context provided here is quite enlightening. It’s amazing how science and technology have led to such important advancements in fuel use.

  4. The elimination of leaded petrol is a victory for public health and environmental protection. Let’s hope we continue to make strides toward cleaner energy solutions.

  5. The comparison table is a great way to visualize the information. It’s hard to believe leaded petrol was so widely used in the past.

  6. Excellent explanation of these two types of petrol. Truly shows how far we’ve come in developing fuel that is better for our planet and our health.

  7. The ban on leaded petrol was a monumental decision that has positively impacted human and environmental health. Glad to see the phase-out and transition to safer alternatives.


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