Editor’s note: An earlier version of this article incorrectly referred to ASTM International as the organization’s prior name, the American Society of Testing and Materials. This name change occurred several years ago.

New testing from AAA has uncovered significant differences in the quality of gasoline sold at fuel retailers in the United States. The independent laboratory testing compared gasolines that met Top Tier standards that were often marketed to consumers as having enhanced, engine-cleaning detergent additives with gasoline brands that do not participate in the automaker-backed program. Top Tier Detergent Gasoline is the premier standard for gasoline performance, established by the Center for Quality Assurance, and backed by automakers such as BMW, General Motors, Fiat Chrysler Automobiles, Honda, Toyota, Volkswagen, Mercedes-Benz and Audi.

Among brands tested, non-Top Tier gasolines caused 19 times more engine deposits than Top Tier brands after just 4,000 miles of simulated driving. Such carbon deposits are known to reduce fuel economy, increase emissions and negatively impact vehicle performance, particularly on newer vehicles. To protect vehicle investments, AAA urges drivers to use a gasoline that meets Top Tier standards for engine cleanliness and performance.

“AAA was surprised to learn the extent to which detergent additives impact gasoline quality,” revealed John Nielsen, AAA’s managing director of Automotive Engineering and Repair. “As advertised, tested Top Tier gasolines kept engines remarkably cleaner than other fuels we tested.”

In response to increasing levels of carbon deposits in modern engine designs, the Environmental Protection Agency mandated a minimum level of detergent for all gasoline sold in the United States in 1996. However, some automakers believe the minimum does not go far enough to ensure optimal vehicle performance and their ability to meet increasingly-stringent fuel economy and emissions requirements. The Top Tier program and performance standard were developed to guarantee that program participants’ gasoline meets stricter targets for engine cleanliness.

“When it comes to selecting a gasoline, automakers got it right – Top Tier gasoline performs best,” continued Nielsen. “By selecting a quality gasoline, drivers can minimize engine deposits, increase vehicle performance and improve fuel economy.”

Despite the fact that two-thirds of U.S. drivers believe there is a difference in quality of gasoline sold by different gas stations, a AAA survey reveals that Americans value convenience and price over quality when it comes to selecting a gas station. Other statistics include:

• Three-quarters of U.S. drivers choose a gas station based on location (75 percent) or price (73 percent).
• Nearly one-third (29 percent) of U.S drivers choose a gas station based on a rewards program.
• Only 12 percent of U.S. drivers select a gas station based on whether the gasoline contains an enhanced detergent package.
• Nearly half (47 percent) of U.S. drivers do not regularly buy gasoline that contains an enhanced detergent additive.
• Men (44 percent) are more likely than women (26 percent) to regularly buy a gasoline that contains an enhanced detergent package, as are baby boomers (41 percent) compared to millennials (32 percent).

“Americans are six times more likely to choose a gas station based on the price of gasoline rather than the quality of the fuel,” continued Nielsen. “Since Top Tier gasoline is widely available and only an average of three cents more per gallon, AAA urges drivers to reconsider their priorities when selecting gas station.”

To ensure a gas station sells a high quality gasoline, consumers should research the fuel options near them. According to Top Tier, one-third of gas stations meet the Top Tier standard for fuel quality. Retailers interested in participating in the Top Tier program can find additional information here.

“Fortunately, consumers can reverse some engine deposits simply by switching gasoline brands,” said Greg Brannon, AAA’s director of automotive engineering. “After a few thousand miles with Top Tier gasoline, performance issues like rough idling or hesitation during acceleration can often be resolved.”

For testing purposes, AAA selected Top Tier and non-Top Tier gasolines from a southern Texas market that represents the type of gasoline sold across the majority of the United States. To measure intake valve and combustion chamber deposits, AAA engaged the services of an independent International Standards Organization 17025 certified engine testing lab to perform an ASTM International standard test on fuels. 

To evaluate consumer gasoline preferences, AAA contracted with a national research company to perform a telephone survey of 1,002 adults (18 years of age and older) living in the continental United States. Survey results are an accurate representation of the total continental U.S. population, 18 years of age and older, with a margin of error of +/- 3.1 percent at a 95 percent confidence level.