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 percent 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 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 percent to 35 percent.
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.
