How to determine the alcohol content of gasoline
The U. S. Department of Energy has an alternative fuels website to aid in locating E85 fuel in your area.
At a minimum, E85 should meet ASTM Specification D 5798. By definition, this means that fuel labeled "E85" will have an ethanol content between 70% and 85%.
To determine how much alcohol has been added by the oil company, you can do the following simple test. Be sure to use adequate ventilation, avoid sparks, heat and any other sources of ignition for liquid gasoline/alcohol AND their vapors!
This is known as "Water Extraction". A graduated glass cylinder, usually 1000 milliliters (ml), is used for this test. Put 250ml of the gasoline to be tested into the graduated flask.
Add 50ml of water to the flask containing the 250ml of sample gasoline.
Seal the top w/a stopper and thoroughly agitate the sample. Let this rest for a couple minutes.
If there's no alcohol in the sample, there will still be only 50ml of water that has separated into a layer at the bottom of the container.
If there IS alcohol present in the sample, the amount of water/alcohol at the bottom of the container will have increased by the amount of alcohol that's present in the 250ml sample.
Subtracting the original 50ml of water that was added at the start of the test from what is now there is the percentage of alky that has been added to the gasoline.