RFA Handbook
By now, many of you know that E15 has been approved and may soon make its way to a pump near you. What some of you don't know is that EPA rules may require you to buy at least four gallons of regular (E10) gasoline. First of all, the four gallon requirement would only apply at stations where E15 is sold from the same hose as E10 gasoline. If each grade of gasoline (E10 and E15) has its own hose, there would be no minimum requirement. However, since many stations have just one hose offering various types of gasoline, you may then be required to pump at least 4 gallons of E10 gasoline to mitigate the higher ethanol concentration left behind in the hose should someone buy E15 ahead of you.

The requirement of at least four gallons in some instances is to protect small engines that need smaller amounts of gasoline from potentially higher concentrations of ethanol from the same hose, should the previous customer bought E15 or higher. After four gallons, the higher concentration of ethanol should have been balanced back out, making purchases of four gallons closer to the E10 standard. But buying say, one gallon of E10 may contain more than 10% ethanol if the customer before you bought E15, because the hose may still have the higher concentration.

A minimum requirement would simply mean more confusion and frustration, and would mean those with small tanks (smaller engines, motorcycles, small boats) may have to find a station that has a separate hose for each various product- something that will require more time to find a station.

In addition, if you aren't careful, or caught on empty pulling into the station, you could be in violation of federal law if you pumped less than the four gallon minimum if there's only the one hose per pump instead of several. That could put thousands of motorists at risk of being in violation of federal law- not something to take lightly- all for simply trying to buy a smaller quantity of fuel.
RFA Handbook

Due to this issue, the station then would not be liable for your mis-fueling, and any engine damage resulting from the gasoline would be on your back. Take a look at the pictures in this blog post to understand further. The top image is one where the station's pumps only have one hose per dispenser and carry the four gallon minimum warning. A station that has separate hoses (seen below) aren't required to have a warning because the concern about too high of ethanol amounts would not apply.

All this information is sure to cause confusion, and perhaps more importantly, could require motorists caught in a bind to purchase at least $15 worth of gasoline, even if they don't have the cash or credit card to buy enough to avoid federal penalty. I'm worried enough about gas prices, the last thing I want to do is have to find a station where it'll be legal to fill with just a couple gallons if I need it! What do you think? Let us know in the comments!