May contain up to 10% ethanol

I did not see a thread that specifically covered this. Also it is more of a vent than anything. I don't believe there's a reasonable solution and I didn't want to clutter up anyone else's thread.
On the "wait list". Using the ScangaugeII on our Avalon while waiting for our Prius. Have been able to bring the Avalon's average mpg around town up a couple of MPG by monitoring the GPH & HPR gauges. Brought average around town from 17-19 MPG up to 19-21 MPG. Switched to Mobil1 on last oil change and increased tire psi from 34/32 to 42/40. Looked like we were going to pick up another MPG or so. Mileage began to fluctuate. Figured it was inconsistant driving habits. Then on last two fillups noticed this label on the gas pump for the first time, metro Atlanta area. "May contain up to 10% ethanol". I do not want to make this a pro vs con ethanol thread. My concern is the "May....". I assume that means that what I am pumping into my cars can contain anything from no ethanol to "up to 10%" ethanol, depending on what was delivered by the last tanker and what was previously in the station tanks. It's just a pain. Just when we were trying to get a handle on how different driving habits, maint., etc affect MPG, they make the energy per gallon variable by tankful. And no, I don't want an ethanol gauge to measure the % ethanol. Besides, if I remember correctly, the gauges accuracy or margin of error is greater than the ethanol's effect would be @ <= 10%. It's just frustrating. I just thought there could be a remote possibility that someone out there might have a suggestion since I believe that Prius owners must represent the largest concentration of people that actually track their MPG. Thank you for letting me vent. I don't expext this thread to last long.

 

Perhaps I need to further clarify my concern. I don't care if it's 0% or 10%, or somewhere in between. I just what to know what it is so that I can keep meaninful mileage records. I knew about the 10% and that's fine if it's going to be 10%. But how are you going to make any sense out of your effort to track your mileage if you don't know what your burning? It's the "May contain up to......" that I have the problem with. Not the "10% ethanol". Perhaps it's just a temporary label during changing over to 10% ethanol. How do the states handle it that change over between summer and winter? How do you know what you're burning.
Thanks for the reply!

 

Thank you for your replies. I am aware of the E10 issues. My concern was "is it or isn't it or where in between is it" for this fillup? How do you know if what your doing is better or worse for your MPG if you don't know the mixture? However, it seems like the issue may go way till October, when they switch back, maybe! If they're filling the station tanks with E10, consistantly, then after a few tanker deliveries, the mixture should become stable. My concern was non-E10 one fillup and E10 on the next would make it difficult to interpret MPG data.
Thanks Again !

 

Evidently my question is still not clear. However, if we are going to E10 that's fine. My post tried to explain that E10 is not the issue. "May contain up to 10% Ethanol" meant an undefined percentage of Ethanol and ethanol does not contain the same amount of energy as gasoline. Ergo, the percentage of ethanol will affect your mileage accordingly. I was trying to test different driving habits, changing to a full synthetic, increasing the psi in the tires, etc. it would help if the fuel mixture was consistant so that I any changes in mpg from tank to tank would be a result of my testing, not variations in the fuel mixture. Hopefully is just temorary during the change over to E10. Then I can go back to fine tuning my driving habits.
Thank you for your input. E10 is fine with me.