Actually, it's the ethanol and additives that is mixed in at the loading rack by the driver. The %ethanol is not guaranteed by law.

However, the octane is.

Octane is tested at the tank farm to guarantee it. Not mixed at the truck, if somebody made a mistake and sold 88 octane instead of 89 octane there would be fines involved.

It is also tested for H2O, with a flame test.

I am pretty sure that the various octane ratings are delivered separately in the pipeline.

As long as a station is busy enough to have frequent deliveries, there should not be a water problem.

"Bad gas" is a red herring these days. I guess it is possible to get 3 month old gas at a very rural station. The station tanks are sealed these days for air quality reasons, so water is not a huge problem anymore. Most stations filter the gas at the pump, so solid contaminants should not be a problem.

In the "olden" days there was a brand that actually did have 2 hoses at the pump to mix a "dial your own" grade, I think it was SunOco.

 

Not to jump off topic here but Don what do you mean exactly by dial your own? Just curious! I only started buying gas for myself in 2009! XD

 

Dial your own mean "select the octane " you want.
Back in the 60's, when I was a teenager, my father owned an oil company that had branded gasoline staions, full service that had blender pumps and you could ask for any mix of five different grades.
The attendant turned a knob on the side of the dispenser just right of the nozzlle holder and rotate it to the grade you needed.
Five different mixes with five different prices. All dispensed through one hose and nozzle.

This was done machanically back in the sixty's.

Only had two underground tanks...Regular and Eythel.

All blending was done in the dispenser.

 

WOW that is pretty interesting/amazing. I wonder why they got rid of these sort of things. MY mother and father were both BORN in the 60's and myself in 1991 so definitely before my time LOL

 

To day you can blend by pumping so much 87 then so much 91 but not much gain or differences, but back then you could get 104 octane and at some Sunoco s 108

 

I remember buying Sunoco 260 (104 octane) for 25 cents a gallon.

 

Now I'm really feeling old! My grand parent were born in the 1800's.