Petrol is the most common type of fuel used in cars today, and is made from a blend of hundreds of different hydrocarbon compounds. Unfortunately, petrol is also one of the major causes of pollution, producing carbon monoxide, carbon dioxide and nitrogen oxides. Not only do these pollutants contribute to global warming, but they can also cause acid rain and can damage human health.

Petrol is given an octane rating (RON) as a measurement of its ability to resist engine knocking, i.e. when the fuel-air mix in the cylinder explodes instead of burning in a controlled way. The higher the octane number; the greater the resistance to engine knocking.

Leaded Petrol

In the past, lead was added to petrol to improve combustion; however it was found to be harmful to the environment and toxic to humans, and as a result, leaded four star petrol was removed from sale on British forecourts on 1st January 2000. However, a small number of licensed dealers are permitted to sell leaded petrol, usually for older cars that are used for circuit racing.

Lead Replacement Petrol (LRP)

Lead Replacement Petrol (LRP) may be found for pre-1992 cars that need the protection the protection of a special additive for their 'soft' cast-iron valve seats. LRP has now been phased out, and separate additives are now sold to treat unleaded petrol instead.

Premium Unleaded

The majority of petrol sold in the UK is 95 octane unleaded petrol- usually termed 'Premium' grade. It is suitable for all petrol cars made since 1992.

Super Unleaded Petrol

Super Unleaded has an octane rating of 97, and is recommended for use in high performance vehicles, or in older vehicles that are unable to run on the lower octane level of Premium Unleaded petrol. However, this type of petrol is more expensive than Premium Unleaded, and many cars will be able to see little, if any improvement in performance.

Ultra Low Sulphur Petrol

Ultra Low Sulphur Petrol (ULSP) contains less than 50 ppm of sulphur, compared with the maximum of 150 ppm allowed in standard petrol. This reduction in sulphur results in lower toxic emissions, and helps to prolong the life and efficiency of catalytic converters in vehicle exhaust systems. The majority of Premium or Super Unleaded petrol sold in the UK is in fact Ultra Low Sulphur Petrol.

However, it should be borne in mind that the increased processing needed at the refineries to produce ULSP uses additional energy, which leads to an increase of CO2 emissions.

Zero Sulphur Petrol

Zero Sulphur Petrol has less than 10 ppm of sulphur, which leads to reduced exhaust emissions and more active exhaust catalysts. This type of fuel is particularly advantageous for direct injection petrol (GDI) engines.

Although the production of zero sulphur fuels involve more processing at refineries, thus increasing carbon dioxide emissions, it is thought that the improvement to fuel economy will be greater than these increase in emissions.

Performance Petrol

There are a number of brands of petrol sold in the UK as performance grades, with octane ratings ranging up to 102. This high octane level means that the petrol burns more completely, which can allow highly tuned turbo charged and high speed naturally aspirated engines to perform at their best. However, this type of petrol only offers an advantage to drivers who use an appropriate type of car, driven vigorously enough to require the performance gains; for example, a private motor sport enthusiast.