The problem with "Top Tier" gas is you're hurting your mileage because the spec mandates between 8-10% ethanol in the fuel. Top Tier is a marketing ploy, because you'll visit those stations more often due to lowered mileage. BP uses an additive package which exceeds Top Tier standards without using ethanol.

 

That, I did not know

 

According to BP's FAQ it does. But... the Top Tier requires ethanol use and that's probably the main reason its not rated, and BP suggests in the FAQ they are doing what's best for the consumer, not what's best for the Top Tier program. I will say this... BP dispenses Amoco formulated fuels, which for decades have been known as good fuel (many of them have little windows on the pumps so you can see that the fuel going is is clear instead of brown).

Who knows for certain? Only way to get past everyone's marketing hype is with testing....