FastMover, the EPA reference you're talking about sounds like http://www.epa.gov/tier2/420f04002.pdf and http://www.epa.gov/greenvehicles/detailedchart.pdf.

I still am wondering where you get this notion of "Tier 1" gasoline from. Are you talking about http://www.toptiergas.com/?

06 Toyota Prius, 04 Nissan 350Z; mom has 07 NAH

www.toptiergas.com is what we are all talking about. The official name is Top Tier. However that site itself refers to the EPA standard gas as Type 2, implying that Top Tier is Type 1. I have no problem with calling it Top Tier or Type 1.

My difficulty in figuring out what Marianne is experiencing, is that, where I live, there are no big differences in price or performance between name brand gas of Top Tier or Tier 2 with the slight exception of Shell.

In NJ, Gas stations tend to be clumped together in groups with practically identical prices or single remote stations with high prices no matter what kind of gas it is. The gas in my town, a no-name brand and a Gulf station are always 10 to 12 cents more expensive then the stations on the big highway. On my way to and from my recreational basketball game last night I passed three EXXON stations, one wanted 3.07 for regular, one wanted 3.03 and one wanted 2.99. The Shell station near my town is about 5 cents higher then the no-name station, but the Shell station on the big highway is 5 cents lower. Stations are independently owned and often have prices that reflect their immediate competition, not a set price. The final result is that Top Tier and tier 2 are about the same price if you average it out. Unfortunately those stations are not conveniently on my way to work.

Performance wise we have never had a tank average better then 38.5 (long drive at the hight of summer) and never lower then 31.8( a blizzard week in the hight of winter) no matter what gas we use. (We normally use BP). Shell gives us a 1 to 2 MPG boost over EXXON and BP. All other gas is about the same. (average of 35 MPG)

If Marianne is averaging 35 MPG at one station, but only 28 at another then I agree something fishy is going on at that 28 station, but it is not that Top Tier gives a 7 MPG improvement over Tier 2. I just don't see it.

There were a lot of posts and threads about it a year or so ago... and they all refered to Top Tier as Tier 1... so it is permanently ingrained in my brain... even if it isn't the correct term.

I would suspect a marketing trick. If Shell is pumping their gas as "better"... but they are focusing on the top tier/cleaner aspects... is their anything they could do that would up the MPG? It would be a lovely marketing trick to put in an additive that upped MPG and make it look like that is a side effect of cleaner gas... especially if you wanted to market into the hybrid community.

I'm a science dud so I can't answer this.