A Brief History of Octane

This fact sheet from the Environmental and Energy Study Institute provides a historical overview of octane additives in U.S. gasoline, detailing the transition from lead and other petroleum-based aromatics to ethanol due to health and environmental concerns. It discusses the role of the EPA in regulating fuel composition to reduce tailpipe emissions and improve engine efficiency.

• Octane is a gasoline additive essential for preventing 'knock'—the premature ignition of fuel in an engine's cylinder—which can damage engines and reduce efficiency. Higher octane ratings allow for higher compression ratios, turbocharging, and engine downsizing, which can increase vehicle efficiency and lower greenhouse gas emissions.
• Tetraethyl lead was the preferred octane provider starting in 1921 due to low costs, despite early warnings of chronic degenerative diseases. The EPA began phasing it out in the mid-1970s after research established devastating health impacts, particularly in children, including low IQ, nerve damage, and behavioral disorders. Between 1927 and 1987, the EPA estimates 68 million children were exposed to toxic lead levels from leaded gasoline.
• Following the lead phase-out, the refining industry increased the use of the BTEX complex (benzene, toluene, ethyl-benzene, and xylene), which are petroleum-based aromatics. BTEX volume in the gasoline pool rose from 22 percent to approximately one-third by 1990, reaching as high as 50 percent in premium grades. Health research suggests low-level exposure to BTEX and its combustion products, such as ultra-fine particulates (UFP) and polycyclic aromatic hydrocarbons (PAHs), can be carcinogenic, mutagenic, and linked to neurodegenerative disorders.
• Methyl tertiary butyl ether (MTBE) was used in 87 percent of reformulated gasoline (RFG) by the late 1990s to reduce ozone precursors. However, it was phased out by 2005 after the EPA and a Blue Ribbon Panel found it threatened groundwater supplies, with the U.S. Geological Survey finding MTBE in 20 percent of groundwater supplies in RFG areas.
• Ethanol is currently a primary octane source in the U.S., with over 95 percent of gasoline sold as E10 (10 percent ethanol). Pure ethanol has an octane rating over 100 and is generally the cheapest octane provider. Increasing ethanol content from 10 to 15 percent is anticipated to reduce cancer risk from tailpipe emissions by 6.6 percent.
• The U.S. government has implemented several policies to mandate renewable fuels, including the Renewable Fuel Standard (RFS) via the Energy Policy Act of 2005 and the Energy Independence and Security Act of 2007, the latter of which targeted 36 billion gallons of renewable fuels by 2022. For 2016, final renewable fuel volumes were set at 18.11 billion gallons.
• A transition to mid-level ethanol blends (between E25 and E40) is proposed to lower fuel costs, standardize supply, and enable the design of highly fuel-efficient engines. The EPA and Department of Energy have already approved E15 for vehicles from model year 2001 and newer, which represent 80 percent of vehicles currently on the road.

APA

Stolark, J. (2016). A Brief History of Octane. Environmental and Energy Study Institute. https://www.eesi.org/papers/view/fact-sheet-a-brief-history-of-octane

Chicago

Stolark, Jessie. A Brief History of Octane. Environmental and Energy Study Institute, 2016. https://www.eesi.org/papers/view/fact-sheet-a-brief-history-of-octane.

Wikipedia

{{cite report |last1=Stolark |first1=Jessie |title=A Brief History of Octane |publisher=Environmental and Energy Study Institute |date=30 March 2016 |url=https://www.eesi.org/papers/view/fact-sheet-a-brief-history-of-octane |access-date=17 August 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{stolark2016brief, author = {Stolark, Jessie}, title = {{A Brief History of Octane}}, institution = {Environmental and Energy Study Institute}, year = {2016}, month = mar, url = {https://www.eesi.org/papers/view/fact-sheet-a-brief-history-of-octane}, urldate = {2026-08-17}, note = {Indexed by Climate Insights Directory} }