Antiknock additives Tetraethyl lead Gasoline, when used in high-
compression internal combustion engines, tends to auto-ignite or "detonate" causing damaging
engine knocking, also called "pinging" or "pinking". To address this problem,
tetraethyl lead (TEL) was widely adopted as an additive for gasoline in the 1920s. With a growing awareness of the seriousness of the extent of environmental and health damage caused by lead compounds, and the incompatibility of lead with
catalytic converters, governments began to mandate reductions in gasoline lead. In the U.S., the
Environmental Protection Agency issued regulations to reduce the lead content of leaded gasoline over a series of annual phases, scheduled to begin in 1973 but delayed by court appeals until 1976. By 1995, leaded fuel accounted for only 0.6 percent of total gasoline sales and under () of lead per year. From January 1996, the
U.S. Clean Air Act banned the sale of leaded fuel for use in on-road vehicles in the U.S. The use of TEL also necessitated other additives, such as
dibromoethane. European countries began replacing lead-containing additives at the end of the 1980s. By the end of the 1990s, leaded gasoline was banned within the entire European Union with an exception for
Avgas 100LL for
general aviation. The UAE started to switch to unleaded in the early 2000s. Reduction in the average lead content of human blood may be a major cause for falling violent crime rates around the world including South Africa. A study found a correlation between leaded gasoline usage and violent crime (see
Lead–crime hypothesis). Other studies found no correlation. In August 2021, the
UN Environment Programme announced that leaded gasoline had been eradicated worldwide, with
Algeria being the last country to deplete its reserves.
UN Secretary-General António Guterres called the eradication of leaded petrol an "international success story". He also added: "Ending the use of leaded petrol will prevent more than one million premature deaths each year from heart disease, strokes and cancer, and it will protect children whose IQs are damaged by exposure to lead".
Greenpeace called the announcement "the end of one toxic era". Leaded gasoline continues to be used in aeronautic, auto racing, and off-road applications. The use of leaded additives is still permitted worldwide for the formulation of some grades of
aviation gasoline such as
100LL, because the required octane rating is difficult to reach without the use of leaded additives. Different additives have replaced lead compounds. The most popular additives include
aromatic hydrocarbons,
ethers (
MTBE and
ETBE), and
alcohols, most commonly
ethanol.
Lead replacement petrol Lead replacement petrol (LRP) was developed for vehicles designed to run on leaded fuels and incompatible with unleaded fuels. Rather than tetraethyllead, it contains other metals such as
potassium compounds or
methylcyclopentadienyl manganese tricarbonyl (MMT); these are purported to buffer soft exhaust valves and seats so that they do not suffer recession due to the use of unleaded fuel. LRP was marketed during and after the phaseout of leaded motor fuels in the United Kingdom,
Australia,
South Africa, and some other countries. Consumer confusion led to a widespread mistaken preference for LRP rather than unleaded, and LRP was phased out 8 to 10 years after the introduction of unleaded. Leaded gasoline was withdrawn from sale in Britain after 31 December 1999, seven years after
EEC regulations signalled the end of production for cars using leaded gasoline in member states. At this stage, a large percentage of cars from the 1980s and early 1990s which ran on leaded gasoline were still in use, along with cars that could run on unleaded fuel. The declining number of such cars on British roads saw many gasoline stations withdrawing LRP from sale by 2003.
MMT Methylcyclopentadienyl manganese tricarbonyl (MMT) is used in Canada and the U.S. to boost octane rating. Its use in the U.S. has been restricted by regulations, although it is currently allowed. Its use in the European Union is restricted by Article 8a of the Fuel Quality Directive following its testing under the Protocol for the evaluation of effects of metallic fuel-additives on the emissions performance of vehicles.
Fuel stabilizers (antioxidants and metal deactivators) s and derivatives of
phenylenediamine are common antioxidants used to inhibit gum formation in gasoline Gummy, sticky resin deposits result from
oxidative degradation of gasoline during long-term storage. These harmful deposits arise from the oxidation of
alkenes and other minor components in gasoline (see
drying oils). Improvements in refinery techniques have generally reduced the susceptibility of gasolines to these problems. Previously, catalytically or thermally cracked gasolines were most susceptible to oxidation. The formation of gums is accelerated by copper salts, which can be neutralized by additives called
metal deactivators. This degradation can be prevented through the addition of 5–100 ppm of
antioxidants, such as
phenylenediamines and other
amines. Gasolines are also treated with
metal deactivators, which are compounds that sequester (deactivate) metal salts that otherwise accelerate the formation of gummy residues. The metal impurities might arise from the engine itself or as contaminants in the fuel.
Detergents Gasoline, as delivered at the pump, also contains additives to reduce internal engine carbon buildup, improve
combustion and allow easier starting in cold climates. High levels of detergent can be found in
Top Tier Detergent Gasolines. The specification for Top Tier Detergent Gasolines was developed by four automakers:
GM,
Honda,
Toyota, and
BMW. According to the bulletin, the minimal U.S.
EPA requirement is not sufficient to keep engines clean. Typical detergents include
alkylamines and
alkyl phosphates at a level of 50–100 ppm.
Brazil The
Brazilian National Agency of Petroleum, Natural Gas and Biofuels (ANP) requires gasoline for automobile use to have 27.5 percent of ethanol added to its composition. Pure hydrated ethanol is also available as a fuel.
Australia Australia uses
E10 (up to 10% ethanol) and E85 (up to 85% ethanol) in its gasoline.
New South Wales mandated biofuel in its Biofuels Act 2007, and
Queensland had a biofuel mandate since 2017. Fuel pumps must be clearly labelled with its ethanol/biodiesel content.
U.S. The federal
Renewable Fuel Standard (RFS) effectively requires refiners and blenders to blend renewable
biofuels (mostly ethanol) with gasoline, sufficient to meet a growing annual target of total gallons blended. Although the mandate does not require a specific percentage of ethanol, annual increases in the target combined with declining
gasoline consumption have caused the typical ethanol content in gasoline to approach 10 percent. Most fuel pumps display a sticker that states that the fuel may contain up to 10 percent ethanol, an intentional disparity that reflects the varying actual percentage. In parts of the U.S., ethanol is sometimes added to gasoline without an indication that it is a component.
India In October 2007, the
Government of India decided to make five percent ethanol blending (with gasoline) mandatory. Currently, 10 percent ethanol blended product (E10) is being sold in parts of the country. Ethanol has been found in at least one study to damage catalytic converters. In July, 2025, India has mandated blending of E20 despite facing backlash.
Dyes Though gasoline is a naturally colourless liquid, many gasolines are dyed in various colours to indicate their composition and acceptable uses. In Australia, the lowest grade of gasoline (RON 91) was dyed a light shade of red/orange, but is now the same colour as the medium grade (RON 95) and high octane (RON 98), which are dyed yellow. In the U.S., aviation gasoline (
avgas) is dyed to identify its octane rating and to distinguish it from kerosene-based jet fuel, which is left colourless. In Canada, the gasoline for marine and farm use is dyed red and is not subject to fuel excise tax in most provinces.
Oxygenate blending Oxygenate blending adds
oxygen-bearing compounds such as
methanol,
MTBE,
ETBE,
TAME,
TAEE,
ethanol, and
biobutanol. The presence of these oxygenates reduces the amount of
carbon monoxide and unburned fuel in the exhaust. In many areas throughout the U.S., oxygenate blending is mandated by EPA regulations to reduce smog and other airborne pollutants. For example, in Southern California fuel must contain two percent oxygen by weight, resulting in a mixture of 5.6 percent ethanol in gasoline. The resulting fuel is often known as reformulated gasoline (RFG) or oxygenated gasoline, or, in the case of California, California reformulated gasoline (CARBOB). The federal requirement that RFG contain oxygen was dropped in May 2006 because the industry had developed
VOC-controlled RFG that did not need additional oxygen. MTBE was phased out in the U.S. due to groundwater contamination and the resulting regulations and lawsuits. Ethanol and, to a lesser extent, ethanol-derived ETBE are common substitutes. A common ethanol-gasoline mix of 10 percent ethanol mixed with gasoline is called
gasohol or E10, and an ethanol-gasoline mix of 85 percent ethanol mixed with gasoline is called
E85. The most extensive use of ethanol takes place in
Brazil, where the ethanol is derived from
sugarcane. In 2004, over of ethanol was produced in the U.S. for fuel use, mostly from
corn and sold as E10. E85 is slowly becoming available in much of the U.S., though many of the relatively few stations vending E85 are not open to the general public. The use of
bioethanol and bio-methanol, either directly or indirectly by conversion of ethanol to bio-ETBE, or methanol to bio-MTBE is encouraged by the European Union
Directive on the Promotion of the use of biofuels and other renewable fuels for transport. Since producing bioethanol from fermented sugars and starches involves
distillation, though, ordinary people in much of Europe cannot legally ferment and distill their own bioethanol at present (unlike in the U.S., where getting a
BATF distillation permit has been easy since the
1973 oil crisis). ==Safety==