The results showed that, on average, non-Top Tier gasoline had 19 times more carbon deposits on injectors, on intake valves, and in the combustion chamber than Top Tier gasoline had.

AAA also found that Top Tier gasoline can have a cleansing effect, reducing intake valve deposits by 45 to 72 percent when used over a 5,000-mile interval. Variation in the results is attributed to the detergents used by different brands.

Further, analyzing gas prices over a 12-month period found just a 3-cent price difference between non-Top Tier and Top Tier gasoline.