Frequent Questions

Where can I locate information about Methyl Tertiary Butyl Ether (MTBE)?

Definitions

Methyl tertiary-Butyl Ether: A flammable liquid with a distinctive, disagreeable odor. It is made from blending chemicals such as isobutylene and methanol, and has been used since the 1980s as an additive for unleaded gasolines to achieve more efficient burning. (EPA Science Vocabulary Glossary)

MTBE is defined under 40 CFR 98: Mandatory Greenhouse Gas Reporting as an oxygenate. 40 CFR 98.6 defines oxygenates as “substances which, when added to gasoline, increase the oxygen content of the gasoline. Common oxygenates are ethanol, methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether (ETBE), tertiary amyl methyl ether (TAME), diisopropyl ether (DIPE), and methanol.”

Clean Air Act Requirements

Since oxygenates can enhance fuel combustion and thereby reduce exhaust emissions, the Clean Air Act requires use of oxygenated gasoline in areas where winter time carbon monoxide levels exceed federal air quality standards. Learn more at Gasoline Winter Oxygenates

Oxygenates can be part of reformulated gasoline (RFG): gasoline blended to burn more cleanly than conventional gasoline and to reduce smog-forming and toxic pollutants in the air we breathe. RFG is required in cities with high smog levels and is optional elsewhere. Learn more at Reformulated Gasoline

Concerns About MTBE

To date, independent expert review groups who have assessed MTBE inhalation health risks (see Interagency Assessment of Oxygenated Fuels) have not concluded that the use of MTBE-oxygenated gasoline poses an imminent threat to public health. However, researchers have limited data about what the health effects may be if a person swallows (ingests) MTBE. So at this point, it would only fall under Secondary Drinking Water Standards for Nuisance Chemicals (aesthetic conditions like taste, color, and odor).

Other Summaries and Information

Because oxygenated fuels are sometimes stored in underground storage tanks (USTs), you can find most of EPA’s information about MTBE’s history and concerns on the UST website:

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