A Brief History of Octane in Gasoline: From Lead to Ethanol

This fact sheet from the Environmental and Energy Study Institute (EESI) outlines the history and evolution of octane additives in United States gasoline, detailing the transition from lead and other petroleum-based aromatics to ethanol due to health and environmental concerns.

• Octane is a gasoline additive used to prevent 'knock,' which is the premature ignition of fuel in an engine's cylinder that can damage the engine and reduce efficiency. Higher octane ratings allow for higher compression ratios and turbocharging, which can increase engine efficiency and lower greenhouse gas emissions by reducing petroleum consumption.
• Tetraethyl lead was the primary octane provider in the U.S. from 1921 until the mid-1970s because it was cheaper to produce than alternatives. However, it was phased out by the EPA due to severe health impacts, particularly in children, including low IQ, nerve damage, and behavioral disorders. The EPA estimates that 68 million children were exposed to toxic lead levels from gasoline between 1927 and 1987.
• Following the lead phase-out, the refining industry increased the use of the BTEX complex (benzene, toluene, ethyl-benzene, and xylene). BTEX volume rose from 22 percent to approximately one-third of the gasoline pool by 1990, reaching up to 50 percent in premium grades. Health research suggests low-level exposure to BTEX may cause cardio-pulmonary, reproductive, and immunological issues, and its incomplete combustion produces carcinogenic ultra-fine particulates (UFP) and polycyclic aromatic hydrocarbons (PAHs).
• 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 U.S. Geological Survey found it contaminated groundwater supplies in 20 percent of 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, making it a cost-effective way for refiners to raise the octane of 'sub-octane gas' to retail standards. Increasing ethanol content from 10 to 15 percent is anticipated to reduce cancer risk from tailpipe emissions by 6.6 percent.
• The document suggests that transitioning to mid-level ethanol blends (between E25 and E40) could standardize the fuel supply, lower consumer costs, 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

Environmental and Energy Study Institute (2016). A Brief History of Octane in Gasoline: From Lead to Ethanol. https://www.eesi.org/files/FactSheet_Octane_History_2016.pdf

Chicago

Environmental and Energy Study Institute. A Brief History of Octane in Gasoline: From Lead to Ethanol. 2016. https://www.eesi.org/files/FactSheet_Octane_History_2016.pdf.

Wikipedia

{{cite report |author=Environmental and Energy Study Institute |title=A Brief History of Octane in Gasoline: From Lead to Ethanol |date=March 2016 |url=https://www.eesi.org/files/FactSheet_Octane_History_2016.pdf |access-date=17 August 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{environmentalandenergystudyinstitute2016brief, author = {{Environmental and Energy Study Institute}}, title = {{A Brief History of Octane in Gasoline: From Lead to Ethanol}}, institution = {Environmental and Energy Study Institute}, year = {2016}, month = mar, url = {https://www.eesi.org/files/FactSheet_Octane_History_2016.pdf}, urldate = {2026-08-17}, note = {Indexed by Climate Insights Directory} }