In the end, every aspect remained virtually the same. There were minute changes for some of the vehicles, but they weren't enough to be noticeable. And for fuel economy, the differences wouldn't even come close to the 23-percent increase in fuel cost AAA estimated for premium. AAA director of automotive engineering Greg Brannon said that the cars did recognize and compensate for the different octane fuels. AAA measured ignition timing in each vehicle with each type of fuel, and there was a noticeable change in timing when premium fuel was used. So it was surprising to the testers that none of the vehicles adjusted timing in such a way that would improve at least one performance aspect. In essence, Americans waste $2.1 billion every single year on premium gas that their cars don't need, AAA says.
There is one minor caveat to this test though. The only thing tested here was the effect of octane on vehicle performance. While spending more on premium won't get you any benefits, there are differences in fuels, but the differences come from fuel quality, not octane. In a test done by AAA earlier this year, it was discovered that fuel that meets TOP TIER standards for fuel detergents and additives are much better for engines. The test revealed that fuel that only meets government requirements for additives left 19 percent more deposits over 4,000 miles compared with the TOP TIER fuel. If you're interested in which brands sell TOP TIER fuel, you can find the list here. So the takeaway here is buy the fuel the manufacturer recommends, and buy it from a TOP TIER brand. This way you'll save money and keep your car healthy.