Gasoline (also called petrol in Europe) is a complex mixture of hydrocarbons obtained from crude oil distillation and processing, as well as and other organic chemicals derived from other energy sources. Modern gasoline is a heavily processed product that can also contain various synthetic components, added to improve its performance and meet the demands of today's advanced engine technology.

Until recently, one such component was lead, which was added to gasoline to boost octane ratings and reduce engine wear. However, leaded gasoline cannot be used on cars equipped with the modern catalytic converters designed to reduce harmful exhaust emissions, as lead very rapidly and permanently annihilates the performance of the catalyst. Furthermore, the realisation that lead emitted from vehicle exhausts was having serious health effects resulted in its being phased out, first in North America and then across Europe and, increasingly, the rest of the world.

1980: Lead phase-out

With the reduction or removal of lead, the octane number, i.e. the ability of petrol to avoid engine "knock", must be raised by other means, such as increasing the concentration of aromatics, optimising the use of components such as alkylates and isomerates or blending high octane oxygenates.

When Europe started to phase down lead octane additives in petrol in the 1980s, many refiners usually replaced them with aromatics, which represented the lowest-cost alternative at the time. Towards the end of the 1990s, new environmental regulations started to limit the aromatic content of gasoline.

Refiners seeking alternative blending components came to rely more on fuel oxygenates: oxygen-rich, cost-effective compounds that act as octane enhancers, with the additional benefit of making gasoline burn more completely, thereby significantly reducing toxic exhaust emissions.