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.

The stations that carry it tend to only carry one brand to begin with. The owner of that brand is generally the one that pays, as they have to submit for testing at their own expense.

It's not always more expensive. All Costco gas is Top Tier, for instance.

They require the brand to use the 2x detergent level for every grade, at every location, to display the Top Tier logo.

I go through a tank of gas every 1-2 days. When I don't fill with Top Tier, my fuel economy goes down on that tank. When I consistently don't fill with Top Tier, my fuel economy goes down even on my next tank of Top Tier. That's when it's time to throw in a bottle of polyetheramine (Techron, Redline, Gumout Regane, etc.) to clean things up.

DI engines unfortunately require deeper, periodic cleaning, as the additive will not reach the valves. But I do not have a DI engine, so the detergent makes a significant difference.

It particularly makes a difference in how often I have to (or do not have to) replace lifters to keep them in spec. This engine has solid, non-adjustable lifters.