I mean the octane tiers at the pump, or what is usually marketed as regular, premium, etc. There are at least two other terms used to describe gas tiers:
- "top tier" - marketing term for gasoline with detergents and whatnot
- tier 3 gas - lower sulfer gas that reduces air pollution
AFAIK, all three terms are independent of each other, so you can have tier 3 gas with or without detergents, in any octane tier you need.