Which Pollutes More – Petrol or Diesel?

Which Pollutes More – Petrol or Diesel?

Which one is safer, petrol or diesel? This is a question passed down from one generation of carmakers and drivers to another. It is an issue that has never been answered and will never have just one definite answer. It’s difficult to find just one answer and explanation because there are many factors involved.

Since it can be a little complicated, the best way to get an answer or an explanation, at least, is to enumerate their similarities and differences. Let’s start by describing each gas.


Diesel fuel’s primary source is crude oil. It is commonly used for heavy-duty trucks, trains, buses, and cars. Named after its founder, scientist-inventor Robert Diesel, it is also sourced from natural gas, animal fat, and biomass. Diesel is also formed when coal turns into liquid (liquefaction).

Diesel-powered vehicles used to be heavily favoured in the UK, including by the government. For decades, it was believed that diesel was the safe choice because its carbon dioxide (CO2) emissions were lower than petrol. The government event had a car tax program that incentivised diesel vehicle users.


Petrol is commonly known as gas or gasoline in the US. Around 50% of the total oil consumption in the UK is credited to petrol, with one vehicle using up as much as a gallon per 50 miles.

Petrol’s composition includes hydrocarbons (hydrogen + carbon). These hydrocarbons have more or less 50 different types, such as pentane, isopentane, butane, and BTEX (benzene, toluene, ethylbenzene, xylenes) compounds.

Initially produced via distillation, petrol was the preferred fuel of those who were looking for high-heat combustion. Aside from road transport, large ships and aeroplanes also use petrol.

Petrol emits carbon dioxide when it is burned.

Diesel and petrol similarities

Diesel fuel and petrol fuel have a few similarities. Here are the common ones:

  • Both are sourced from crude oil
  • They have similar by-products: carbon dioxide, particulate matter (PM), sulphur oxides (SO2), and nitrogen oxides (NO2)
  • Both can cause dangerous environmental and health impacts

Diesel and petrol differences

There are also several differences between the two fuel types. Here are some:

  • Diesel is denser (in energy) than petrol on a per gallon/litre basis by at least 10% and 15%
  • Petrol is lighter compared to diesel
  • Petrol consists of short-chain hydrocarbons (5-12) while diesel’s carbon atoms total between eight and 21
  • Petrol engines fall under spark-fired engines while diesel-powered engines are compression-fired engines; spark-fired engines rely on spark plugs to ignite the engine cylinder’s fuel while the cylinders in compression engines auto ignite after fuel is compressed
  • Compression engines, such as diesel, emit lower levels of pollution and are therefore more efficient
  • Diesel is more fuel efficient than petrol and emits lesser carbon dioxide per mile; petrol emits carbon monoxide, diesel does not
  • Diesel-powered vehicles release higher levels of particulate matter and are known for containing nitrogen oxides (NOx); both are toxic
  • Petrol fuel contains lesser fine particles

The Dieselgate diesel emissions scandal has also made authorities believe that diesel carmakers hide true emissions from their customers.

Diesel and petrol – which one is better?

Can one decide which gas pollutes more by just looking at their similarities and differences? Probably, but it’s not easy. Both diesel and petrol are contributors to pollution and impact human health. Their by-products are the same.

Diesel may be more fuel efficient than petrol, but this doesn’t mean it’s better and safer. Petrol has few fine particles, but it’s not a validation that it is a lesser pollutant than diesel.

The safest option for carmakers and car owners is the EV or electric vehicle.

The Diesel emissions scandal

The current reputation of diesel vehicles is due in large part to the diesel emissions scandal. Officially known as Dieselgate, the scandal originally involved only the Volkswagen Group. US authorities allegedly discovered defeat devices in Audi and Volkswagen diesel vehicles in America. They ordered the carmaker to recall the thousands of affected vehicles. Since then, VW has spent billions to pay off fines and fees, as well as to compensate affected drivers.

Defeat devices are illegal because they manipulate emissions levels during regulatory testing so the vehicles can easily pass the test. They can sense when a vehicle is being tested and that’s when they lower emissions to within the legal limits. Regulators will see the vehicles as safe since they are emissions-compliant. However, this is true only during testing conditions.

When the vehicles are brought out for real-world road driving, they emit excessive amounts of NOx. As such, drivers are exposed to dangerous, life-threatening pollutants. Exposure to NOx emissions can result in a person developing various health conditions, including serious ones such as COPD (Chronic Obstructive Pulmonary Disease), cancer, cardiovascular disease, and premature death.

Other carmakers were also involved in the scandal, including BMW, Vauxhall, Nissan, and Renault. Authorities recommend that drivers initiate a diesel claim levelled against their carmakers.

What should I do with my diesel claim?

A diesel claim is your legal right, an opportunity for you to claim compensation for the inconveniences that your carmaker subjected you to. However, before you can do so, you have to visit Emissions.co.uk first so you can check that you are eligible to file a claim. Only then can you start working on your case with the help of emissions experts.