unleaded gasoline

Also known as: lead-free gasoline

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July 14, 2026

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Unleaded gasoline is fuel for internal-combustion engines that is not treated or mixed with lead or lead compounds. For much of the 20th century, tetraethyl lead (TEL) was added to gasoline as an antiknock agent to improve engine performance. However, TEL is a toxic compound containing lead, and its use was phased out starting in the 1970s due to concerns about lead poisoning and its interference with pollution-control devices in automobiles.12

The shift to unleaded gasoline was also driven by environmental legislation, particularly the need to use catalytic converters to reduce smog, as lead interferes with their function. While leaded gasoline was once universally employed, it is now banned in the United States, the European Union, and many other countries.23

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petroleum refining
Octane rating
Since the advent of unleaded fuels in the mid-1970s, however, motor octane measurements have frequently been found to limit actual engine performance. As a result a new measurement, road octane number, which is a simple average of the research and motor values, is most frequently used to define fuel…
Read More
Since the advent of unleaded fuels in the mid-1970s, however, motor octane measurements have frequently been found to limit actual engine performance. As a result a new measurement, road octane number, which is a simple average of the research and motor values, is most frequently used to define fuel…
Read More