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Leaded Petrol vs. Unleaded Petrol: What's the Difference?

Edited by Aimie Carlson || By Harlon Moss || Published on December 30, 2023
Leaded petrol contains the toxic additive tetraethyl lead, while unleaded petrol is free from lead, making it environmentally safer.

Key Differences

Leaded petrol contains tetraethyl lead, which boosts octane rating but is toxic, posing health risks. On the other hand, unleaded petrol, free from lead, is less harmful to health and the environment.
Leaded petrol releases lead particles into the air, contributing to air pollution and health hazards. Whereas, unleaded petrol, by eliminating lead, reduces these environmental and health risks.
Older vehicles, designed for leaded petrol, used lead as a lubricant for engine parts. Modern vehicles are designed for unleaded petrol, with engines and fuel systems incompatible with leaded fuel.
Leaded petrol was initially favored for its high octane level, improving engine performance. In contrast, unleaded petrol, with advancements in refining, matches performance levels without harmful emissions.
Leaded petrol has been phased out globally due to its environmental and health impact. Unleaded petrol is now the standard, in line with global environmental policies.

Comparison Chart


Contains tetraethyl lead
Free from lead

Environmental Impact

Causes air pollution, toxic to humans and wildlife
Less harmful to the environment

Engine Compatibility

Compatible with older vehicles
Used in modern vehicles


High octane, but toxic emissions
Comparable performance, cleaner emissions

Global Regulations

Largely phased out due to health and environmental concerns
Standard fuel type, supported by environmental policies

Leaded Petrol and Unleaded Petrol Definitions

Leaded Petrol

Previously used for its engine knocking prevention properties.
Leaded petrol was initially popular for preventing engine knocking.

Unleaded Petrol

Standard automotive fuel without lead additives.
Unleaded petrol is the only option available at most modern gas stations.

Leaded Petrol

Petrol used in older cars designed for high-octane fuel.
His vintage car still runs on leaded petrol.

Unleaded Petrol

Often contains additives to enhance performance, but not lead.
Unleaded petrol in my car improves performance while being eco-friendly.

Leaded Petrol

Phased out in most countries due to environmental concerns.
The gas station no longer sells leaded petrol due to regulatory changes.

Unleaded Petrol

Conforms to global environmental regulations.
The use of unleaded petrol aligns with global efforts to reduce pollution.

Leaded Petrol

Fuel with tetraethyl lead added to boost octane rating.
Leaded petrol was common before the awareness of its health risks.

Unleaded Petrol

Environmentally safer fuel, reducing air pollution.
The switch to unleaded petrol has had a positive impact on air quality.

Leaded Petrol

Fuel that contributes to air pollution due to lead emissions.
The use of leaded petrol significantly increased air pollution levels.

Unleaded Petrol

Compatible with modern vehicle engines.
All new cars are designed to run on unleaded petrol.


Is unleaded petrol more expensive than leaded?

The price can vary, but unleaded petrol is generally competitively priced.

Why was lead added to petrol?

Lead was added to petrol to increase its octane rating and prevent engine knock.

Can leaded petrol damage modern engines?

Yes, leaded petrol can damage the catalytic converters in modern engines.

What are the health risks of leaded petrol?

Leaded petrol poses risks like neurological damage and respiratory issues.

Why is unleaded petrol preferred?

Unleaded petrol is preferred due to its lower environmental and health impacts.

What is leaded petrol?

Leaded petrol is gasoline with tetraethyl lead added to improve octane rating.

What makes unleaded petrol environmentally friendly?

The absence of toxic lead additives makes it more environmentally friendly.

Is there a performance difference between leaded and unleaded petrol?

Modern unleaded petrol matches the performance of leaded petrol without its harmful effects.

Can I use unleaded petrol in an old car?

Yes, but you might need additives to protect the engine designed for leaded petrol.

Is leaded petrol still available?

Leaded petrol is largely phased out and unavailable in most countries.

Are there any alternatives to leaded petrol for older cars?

Older cars can use unleaded petrol with an additive to protect the engine.

How can I tell if my car requires unleaded petrol?

Check your vehicle’s manual or look for labels near the fuel cap.

What are the consequences of using leaded petrol in a no-lead car?

It can lead to engine damage and void vehicle warranties.

How does unleaded petrol impact the environment?

Unleaded petrol reduces air pollution compared to leaded petrol.

How does unleaded petrol affect fuel efficiency?

Unleaded petrol generally provides similar fuel efficiency to leaded petrol.

Does unleaded petrol improve engine life?

Yes, it can improve engine life by reducing harmful deposits.

What happens if I use leaded petrol by mistake?

It can damage the catalytic converter and affect engine performance.

Can unleaded petrol be used in all types of vehicles?

Unleaded petrol is suitable for most modern vehicles.

What was the main reason for phasing out leaded petrol?

The main reason was its detrimental impact on health and the environment.

What should I do if unleaded petrol isn't available?

It’s best to use unleaded petrol, but if unavailable, seek a compatible alternative.
About Author
Written by
Harlon Moss
Harlon is a seasoned quality moderator and accomplished content writer for Difference Wiki. An alumnus of the prestigious University of California, he earned his degree in Computer Science. Leveraging his academic background, Harlon brings a meticulous and informed perspective to his work, ensuring content accuracy and excellence.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

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