<P> Almost all countries in the world have phased out automotive leaded fuel . In 2011 six countries were still using leaded gasoline: Afghanistan, Myanmar, North Korea, Algeria, Iraq and Yemen . It was expected that by the end of 2013 those countries would ban leaded gasoline, but it has not occurred . Algeria will replace leaded with unleaded automotive fuel only in 2015 . Different additives have replaced the lead compounds . The most popular additives include aromatic hydrocarbons, ethers and alcohol (usually ethanol or methanol). For technical reasons 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 would be technically infeasible to reach without the use of leaded additives . </P> <P> Gasoline, when used in high - compression internal combustion engines, tends to autoignite (detonate) causing damaging "engine knocking" (also called "pinging" or "pinking"). To address this problem, tetraethyllead (TEL) was widely adopted as an additive for gasoline in the 1920s . With the discovery of the extent of environmental and health damage caused by the lead, however, and the incompatibility of lead with catalytic converters, leaded gasoline was phased out in the USA beginning in 1973 . By 1995, leaded fuel accounted for only 0.6% of total gasoline sales and under 2000 short tons (1814 t) of lead per year in the USA . From 1 January 1996, the U.S. Clean Air Act banned the sale of leaded fuel for use in on - road vehicles in the USA . The use of TEL also necessitated other additives, such as dibromoethane . First European countries started replacing lead by the end of the 1980s and by the end of the 1990s leaded gasoline was banned within the entire European Union . Reduction in the average blood lead level is believed to have been a major cause for falling violent crime rates in the United States and South Africa . A statistically significant correlation has been found between the usage rate of leaded gasoline and violent crime: taking into account a 22 - year time lag, the violent crime curve virtually tracks the lead exposure curve . </P> <P> Lead replacement petrol (LRP) was developed for vehicles designed to run on leaded fuel and incompatible with unleaded . Rather than tetraethyl lead 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 . </P> <P> 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 widespread mistaken preference for LRP rather than unleaded, and LRP was phased out 8 to 10 years after the introduction of unleaded . </P>

In the us we specify how effectively a car uses gas