Methyl Tert-Butyl Ether, commonly known as MTBE, once played a significant role in the United States' fuel industry. Introduced as a solution to improve gasoline quality and reduce air pollution, MTBE quickly became a standard additive. Its primary function was to increase the octane rating of gasoline, a property crucial for preventing engine knocking and ensuring smooth operation. Furthermore, MTBE acted as an oxygenate, meaning it introduced oxygen into the gasoline blend. This oxygen content facilitated a more complete combustion process, leading to a significant reduction in harmful emissions, particularly carbon monoxide.

The widespread adoption of MTBE was significantly influenced by the Clean Air Act Amendments of 1990. These amendments mandated the use of reformulated gasoline (RFG) in areas with severe ozone pollution. RFG was required to contain at least 2% oxygen by weight, a requirement that MTBE effectively met. Refiners embraced MTBE due to its cost-effectiveness and compatibility with existing infrastructure, making it the dominant oxygenate for many years. The move away from tetraethyl lead as an anti-knock compound also paved the way for alternatives like MTBE.

However, the success of MTBE in improving air quality was soon overshadowed by growing environmental concerns, primarily related to its impact on water resources. MTBE is highly soluble in water and does not readily biodegrade. When gasoline containing MTBE leaked from underground storage tanks, particularly at gas stations, it could quickly contaminate groundwater sources. This contamination rendered drinking water supplies unusable due to MTBE's distinctive and unpleasant taste and odor, even at very low concentrations. Several municipalities faced significant challenges, with some forced to shut down wells and seek alternative water sources. This led to increased research into MTBE remediation techniques, aiming to remove or neutralize the contaminant from affected water bodies.

In response to these environmental issues, many states began to ban or severely restrict the use of MTBE. The federal government eventually removed the oxygenate requirement for RFG in 2005 through the Energy Policy Act. This legislative change, coupled with the growing awareness of MTBE's environmental drawbacks, prompted a wholesale switch in the industry towards ethanol as the primary fuel oxygenate. While ethanol also presents its own set of challenges, the transition marked the beginning of the end for MTBE's reign as a major fuel additive. Examining the history of MTBE fuel additive use provides valuable lessons on the unintended consequences of chemical innovations and the importance of considering the full life cycle impact of industrial products.