TOP TIER™ gas is gasoline (and also diesel fuel when applicable) that has been certified to meet specific performance standards. A group of automakers -- Volkswagen, Toyota, Honda, General ...

But if the brand is listed on the Top Tier website, all stations selling that brand should be dispensing Top Tier gas in all grades (regular, mid-grade and premium).

Top Tier fuels feature more of these additives than regular gas. In 1995 the Environmental Protection Agency (EPA) set a minimum standard for gasoline additives.

The Costco gas sold at most Costco gas stations is actually of very high quality. The proof of this is that Costco's gas in its major markets meets TOP TIER™ performance standards.