Originally Posted by ProfessWRX
That's because most gas stations are privately owned and only carry the fuel of the big company. Then there's the fuel distributors that move the fuel. Then there's the parent fuel company. Twice removed from the actual data and the actual parent company doesn't care to share their formula with you. Then there's the fact that there are variances regardless. Fuel in the tanks is never empty, rain water dilutes it sometimes, testing done on site also gets put back in the tanks. There IS no exact number. There is not a single person who can tell you the correct answer except somebody that will test on site.
There's your precise answer.
This is true however the distributor does not blend their own formula. Neither does the gas station owner. Someone must know. There is some contamination at the site but that should not account for a major change in the ratios. It's not like the gas is half rain water. I bet ya whatever the producer put in is pretty close to what we get at the station. I understand that there are probably some variations between batches but I also find it hard to believe that the contents vary wildly between production runs. No one makes products like that on mass scale. Shell cannot pump out a 10% ethanol blend and follow it up by a 25% blend because the blending goblin had too much to drink the night before and dumped a few extra barrels into the pot. I bet the mixture is probably very consistent. Unless you're intimately involved with this process, your guess is as good as mine and I think mine is better than yours
Anyways, one way to find out: http://www.fuel-testers.com/
For academic reasons, I am thinking about picking up a kit and doing a once a month sampling of my local Shell station that I usually gas up at. The place was built very recently so I am hoping it does not suffer from long term exposure and contamination.