Timeline: When Ethanol Replaced MTBE in U.S. Gasoline

Ethanol effectively replaced MTBE in most U.S. gasoline in spring 2006, with an earlier shift in key states such as California and New York on January 1, 2004. The nationwide change accelerated after the Energy Policy Act of 2005 removed a federal oxygenate mandate and growing state bans and liability concerns led refiners to drop MTBE in favor of ethanol.

Background: Why the Switch Happened

MTBE (methyl tert-butyl ether) was widely adopted in the 1990s to meet Clean Air Act requirements for cleaner-burning reformulated gasoline. But as evidence mounted that MTBE contaminated groundwater and drinking supplies, states began banning it. Ethanol, a bio-based oxygenate with a far lower groundwater persistence profile, emerged as the practical replacement—especially once federal rules changed to facilitate the transition.

Key Dates and Milestones in the United States

The following timeline highlights the policy and market events that drove the replacement of MTBE with ethanol in U.S. gasoline.

• 1990: Clean Air Act Amendments establish reformulated gasoline (RFG) with oxygen content requirements, prompting widespread MTBE use in the 1990s.
• Late 1990s–early 2000s: Groundwater contamination incidents lead states to act; liability concerns intensify for refiners and retailers.
• January 1, 2004: California and New York bans on MTBE take effect, effectively shifting those states’ gasoline to ethanol blending.
• August 8, 2005: Energy Policy Act of 2005 signed, creating the Renewable Fuel Standard (RFS) and paving the way to remove the federal oxygenate requirement.
• May 5, 2006: EPA rule removing the RFG oxygen content requirement takes effect; refiners rapidly end MTBE use to avoid liability.
• Spring–summer 2006: Industry-wide switch to ethanol in RFG markets nationally; EIA data show MTBE use collapses as ethanol blending surges.
• 2007 onward: E10 (gasoline with up to 10% ethanol) becomes the norm nationwide; MTBE use in U.S. gasoline effectively disappears.

Taken together, these actions moved the market from a patchwork of state bans to a swift, national pivot in 2006, making ethanol the predominant oxygenate in U.S. gasoline.

How the Transition Unfolded

Regional Bans Led the Way

California and New York, two of the nation’s largest gasoline markets, implemented MTBE bans in 2004, compelling suppliers to blend ethanol instead. Other states quickly followed with prohibitions or restrictions, compressing MTBE’s market footprint even before the federal oxygenate requirement was lifted.

A Nationwide Changeover in 2006

With the EPA’s removal of the oxygen content requirement effective May 2006 and the RFS encouraging renewable blending volumes, refiners and distributors rapidly dropped MTBE. By the start of the 2006 summer driving season, ethanol had replaced MTBE in most reformulated gasoline nationwide, a shift reflected in federal energy data and retail supply patterns.

Beyond the U.S.: A Mixed Global Picture

Elsewhere, the timeline varies. Some Canadian provinces restricted or banned MTBE in the early 2000s, nudging more ethanol blending. In parts of Europe, MTBE continued to be used, and ETBE (ethyl tert-butyl ether, made from ethanol) gained ground. There is no single global “replacement date”; policies and fuel specifications remain region-specific.

Why Ethanol Became the Successor

Ethanol provided a technically viable oxygenate, compatible with existing fuel infrastructure when blended at low levels (such as E10). It avoided MTBE’s groundwater contamination profile, and it aligned with federal policy goals under the RFS to expand renewable fuel use. Economics, legal liability, and public health considerations reinforced the move.

What It Means Today

Today, nearly all U.S. gasoline is E10, with E15 expanding in many markets and higher blends like E85 available for flex-fuel vehicles. MTBE is rarely used in the United States, though it remains part of the fuel slate in some other countries depending on local regulations and market conditions.

Summary

Ethanol replaced MTBE in much of the United States by spring 2006, following state bans (notably California and New York in 2004), the Energy Policy Act of 2005, and the EPA’s removal of the RFG oxygenate requirement effective May 5, 2006. The transition was rapid and durable, establishing ethanol—primarily as E10—as the standard oxygenate in U.S. gasoline ever since.

When was MTBE eliminated from gasoline?

The U.S. Congress passed a law that stated the federal government would not offer liability protection for oil companies still using MTBE in fuel by May 2006, which caused MTBE to be completely phased out as a fuel oxygenate.

When did gas stations start using ethanol?

Ethanol was first commercially added to gasoline in the 1920s and its use increased during World War II and the late 1970s as a result of oil embargoes and the phase-out of lead as an octane booster. By 1978, the U.S. EPA allowed for 10% ethanol blends in gasoline (gasohol), and widespread adoption was later driven by the need for octane enhancers to replace lead and the introduction of oxygenate mandates to improve air quality in the 1990s, according to Quora. 
Early Use & Growth

• 1920s-1930s: The first commercial use of ethanol as an octane booster and fuel additive by companies like Standard Oil began. 
• World War II: Ethanol was used as a supplement to domestic gasoline supplies during the war. 
• 1970s: With the phase-out of lead in gasoline and oil embargoes, interest in ethanol as an alternative octane booster resurfaced, according to Quora and NDSU. 
• 1978: The EPA allowed a 10% ethanol blend in gasoline, and the term “gasohol” was defined. 

Mandates & Widespread Adoption

• 1980s: Due to ground water contamination from MTBE, ethanol and other oxygenates were added to gasoline in some states to reduce emissions. 
• 1990-1992: The Clean Air Act Amendments mandated the use of oxygenates like ethanol in certain areas, leading to national programs requiring ethanol blends for air quality reasons. 
• 2005: The Renewable Fuels Standard (RFS) was enacted, setting requirements for the use of renewable fuels, including ethanol, in the U.S. 

What replaced MTBE?

Ethanol was the fuel additive replacement for MTBE.

Why did we stop using MTBE?

MTBE was phased out and eventually banned in many places due to severe groundwater contamination from leaking storage tanks, its high mobility in water, and the offensive taste and odor it imparted to drinking water even at low concentrations. While initially added to gasoline to improve air quality and engine performance, the environmental risks to water supplies became a greater concern, leading to state-level bans and a nationwide phaseout by 2006, with ethanol replacing it as the primary oxygenate. 
Why MTBE was used:

• Air Quality: Opens in new tabIn the 1990s, the Clean Air Act mandated oxygenated gasoline in areas with high air pollution, and MTBE was added to meet these requirements and reduce harmful emissions. 
• Engine Performance: Opens in new tabMTBE also increased gasoline’s octane number, which helped prevent engine knocking. 

Why MTBE was banned:

• Groundwater Contamination: Opens in new tabMTBE is more soluble, mobile, and less biodegradable in water than other gasoline components, meaning it easily spreads through groundwater from leaking tanks. 
• Drinking Water Issues: Opens in new tabThe high mobility meant that MTBE contaminated drinking water supplies even at very low concentrations, producing an offensive taste and odor that made the water unusable for consumption. 
• Costly Remediation: Opens in new tabCleaning up MTBE contamination from water supplies and the environment was expensive, leading to significant financial burdens for communities and oil companies. 

The Outcome:

• Many states and ultimately the federal government initiated a phaseout of MTBE, with California banning it in 2002 and a nationwide phaseout occurring by 2006. 
• The elimination of MTBE in gasoline led to a significant increase in the use of ethanol as the primary replacement oxygenate.