I bought an inexpensive graduated cylinder set on Amazon for various reasons so I decided to test the alcohol content of my fuel today. The last two tanks were run with E0 91 octane from Kwik Trip. Today I filled up with 11.2 gal(13.5 tank size)of E15 88 octane that I normally use. VW gives their blessing on up to E15 and that's my normal fill because it gets the same mileage as E10 and E0 in my testing over the last year. It's consistently $0.05/ gallon less than E10. That's about 2 tanks for free a year for me. Using the instructions from Delphi I took 2 mL of water and added it to 10mL of fuel drawn from the tank of my GTI and shook it up. Subtracting the initial amount of water it read around 9% ethanol content. I plan on testing again after using this tank.