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Lead is one of the most well-known octane additives in the United States so it has a long history. But, there have been other additives used instead of lead due to its health concerns. These include MTBE, BTEX, and ethanol.

Methyl tertiary butyl ether (MTBE)

The Clean Air Act Amendments (CAAA) of 1990 brought new regulations into the oil and gas industry. One thing these new rules required is that any operation that does not meet ground-level ozone standards reformulated gasoline or RFG. Although there was no standard oxygenate used after the CAAA was enacted, by the late 1990s, methyl tertiary butyl ether (MTBE) was used in 87% of RFG.

MTBE was easy to acquire and use, which is why it was so popular. Despite this, it had to be phased out of the industry because of its solubility within water, which resulted in damage to water sources in some areas. By 2005, the EPA reported that MTBE was not being used as a major octane additive.

Here is a brief history of the phaseout of methyl tertiary butyl ether in the United States.

  1. In 1998, the EPA held a Blue Ribbon Panel that showed MTBE can harm groundwater supplies. In areas that used reformulated gasoline, 20% of the groundwater was found by the U.S. Geological Survey (USGS) to have MTBE present.
  2. In 2000, the EPA announced the phase-out of MTBE and along with the Department of Agriculture (USDA), supported the use of ethanol instead.
  3. Between 2000 and 2005, 17 states banned or limited the use of MTBE in the supply of gasoline.

BTEX complex

This is a mixture of benzene, toluene, xylene, and ethyl-benzene. Also known as gasoline aromatics, BTEX is developed from low-octane petroleum products. It is used as an additive to increase the octane levels in gasoline. When lead was phased out, refiners offered both BTEX and ethanol as alternatives. By 1990, BTEX formed up to 50% of gasoline.

Negative health effects of BTEX

As with MTBE and lead, health concerns caused the government and the industry to regulate the use of BTEX. This additive was found to be harmful, even at low-level exposure. Side effects include cardio-pulmonary effects and negative developmental, immunological, and reproductive responses.

The combustion of gasoline with BTEX octane additives results in ultra-fine particulates (UFPs) and polycyclic aromatic hydrocarbons (PAHs). These bring their own negative health effects, including developmental issues, cardio-pulmonary issues, and cancers. UFPs and PAHs are carcinogenic and mutagenic, so regulation has been necessary. Here is a timeline of some of that regulation.

  1. When Congress enacted the Clean Air Act Amendments, refiners had to limit the amount of benzene used in gasoline.
  2. In 2007, the EPA updated the Control of Hazardous Air Pollutants from Mobile Sources (MSAT2) to limit the amount of benzene in gasoline to 0.62%. Other aromatics in BTEX, including toluene and xylene, are not capped.


Henry Ford actually created the first Model T to use ethanol as fuel. Gasoline was the most popular fuel at the time, though, and the industry was not accepting of an alternative fuel that would act as competition. When the oil embargo of 1973 began, fuel prices increased and there were shortages as well. This brought interest to renewable fuels like ethanol and fuel efficiency. Today, most ethanol is mixed with gasoline in the form of E10 (10% ethanol and 90% gasoline).

Using ethanol as an octane additive

Ethanol has lower lifecycle greenhouse gas emissions than normal gasoline and works to boost octane. Pure ethanol has an octane rating of over 100, but refiners are creating gasoline with less than the required octane levels. Then, they add ethanol before it reaches the pump to get the octane level of 87.

Health concerns surrounding ethanol

Although it burns faster than other octane additives, ethanol is cleaner when it burns than other petroleum-based additives. The negative health effects of ethanol are lower compared to BTEX. Even a small increase of ethanol in gasoline from 10 to 15 percent would reduce cancer risks from emissions by 6.6%.

A brief timeline of the ethanol phase-in

  1. In 1975, congress enacted the Energy Policy and Conservation Act (EPAct), establishing Corporate Average Fuel Economy (CAFE) standards for trucks and cars.
  2. In 1988, the Alternative Motor Fuels Act (under CAFE) established incentives for alternative fuel vehicles.
  3. The Energy Policy Act of 1992 was established to define alternative fuels and create federal programs to support the research and use of these fuels.
  4. The Energy Policy Act of 2005 established the Renewable Fuel Standard (RFS), which set a standard minimum volume of renewable biofuels in transportation fuel.
  5. In 2007, the Energy Independence and Security Act (EISA) was passed to increase the volume of renewable fuels under RFS to 36 billion gallons by 2022.
  6. In 2013, the EPA proposed a reduction in the volume of renewable fuels under the RFS, pointing to the lack of infrastructure for renewable fuels.

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