Petrol is probably the best known of all the products from crude oil. Just under 20% of a barrel of crude oil goes to making petrol - the largest proportion for a single product.

Petrol (also called gasoline) is made from the fraction that we call naphtha. Petrol is the product and naphtha is what comes out of the distillation column. It is a mixture of hydrocarbons with between 5 and 10 carbons in their chains

Of all the products, petrol probably has the most branching journey through the refinery. The final blending process takes naphthas and additives that have come from a number of sources.

This is partly because naphthas are produced by the crackers as well as the distillation columns. But also because of the treatments that they receive along the way.

The aim is to produce a high performance fuel with a good anti-knock response and low emissions (including sulphur and lead).

Buses and lorries use diesel oil. This is thicker and less runny than petrol but not as sticky as lubricating oils.

It is slightly cheaper because it isn't used as much. Therefore, some people choose cars that use diesel.