here in California there are basically three grades of gasoline. you have 91 octane and 87 base grade and a mid grade 89 that is blended from the other two. Not long ago I was in Florida at a station that offered 5 different grades and I wondered if all five were actually separate tanks or if all of the three mid grades were blends of the highest and lowest like our mid grade is.
seems to me there is more risk of getting something other than what you think you are getting of it is a blend. Fuel straight from a tank either the highest or lowest should be just that, when it comes to mixing to get a final product that seems like it would be easily to get mixed up especially if one of the primary tanks was running out in not giving the full percentage required to get what is needed
This is the reason the American Motorcyclist Association is opposed to E15 being sold in Blender pumps allowing the same pump to dispense E10 and E15 fuel. If the previous vehicle filled up on E15, however much E15 fuel is still in the line will end up in the next vehicle's tank and and will be diluted by any additional E10 fuel pumped in or that was already in the tank. Vehicles with more limited fuel tank volumes common to gas mowers, gas-powered tools (chainsaws, blowers, etc.) and recreational vehicles such as snowmobiles, Personal Watercraft and motorcycles, are more susceptible to getting a large dose of E15 fuel with possibly disastrous consequences over time since these vehicles are not typically designed to run concentrations above E10 fuel and could experience failure with constant exposure to additional ethanol from the extra E15 fuel in the pump hose/handle.