In the U.K., there are currently three main types of driving gas (known in Britain as "petrol") for sale at petrol stations. Unleaded petrol is sold in 95 octane and 97 octane versions, and diesel remains a popular fuel source for commercial vehicles, as well as for some private passenger vehicles. The purity of these driving fuels is regulated by both European and U.K. authorities. The European Fuels Directive 98/70/EC governs the allowable chemical composition of each fuel, and this directive was adopted as U.K. law in 1999 through the Motor Fuels (Composition and Content) Regulations. Different types of fuel must meet the additional British Standards.
95 octane unleaded fuel must meet the requirements of British Standard BS EN 228:2004 (updated in 2008), and 97 octane unleaded fuel must meet British Standard BS 7800:2004. Additionally, European directive 98/70, which became effective on January 1, 2000, specifies that unleaded petrol must have no more than 150 parts per million of sulphur. Aromatics in the fuel are limited to a maximum of 42 per cent of the fuel's volume. Aromatics are compounds that occur naturally in the oil from which driving gas is derived, but they may be harmful and pollutant. In particular, it is desirable to limit the amount of the aromatic compound benzene present in driving fuels.
Low Sulphur Unleaded Petrol
Low-sulphur versions of each fuel were introduced in the U.K. ahead of the dates required by directives. Low-sulphur fuels improve air quality. The "ultra low sulphur" variety of 95 octane or 97 octane unleaded petrol may have only a maximum of 50 sulphur parts per million, and the maximum aromatics percentage is reduced from 42 per cent to 35 per cent.
Diesel fuels must comply with British Standard BS EN 590:2004. Furthermore, a maximum sulphur content of 350 parts per million is allowed by European directive 98/70/EC, although for low-sulphur diesel, this limit is reduced to 50 ppm. More recently, 10 ppm ultra-low sulphur fuels have been developed. Diesel for sale in the U.K. is also limited in terms of maximum fuel density, currently the upper limit is 835 kilograms per cubic meter.