You can test if gasoline contains ethanol with the water extraction method (the water extracts the ethanol from the gasoline).

We've been using 10% EtOH mix here in IL since the early 70s: I've never had a problem with it in any engine from my lawn mower to a Lamborghini.

Stabil absorbs moisture and it turns into a gooey mess that is more trouble than the moisture would have been by itself. Beware. If you insist moisture is a problem for you, then either drain the tank when the engine is not in use, or, just keep it full so moisture doesn't condense on the inside of the cool, air exposed tank walls.

It's been known for decades that gas mileage is greatly improved and engine carbon deposits can be eliminated by burning a fuel/air/water droplet mix. (The source of that "100mpg carburetor" that BigOIl has supposedly kept off the market all these years myth.) The only drawback is that the blow-by of the water fouls the oil, leading to premature engine wear. Oh well. Back to the drawing boards.

@doc: water injection is an old idea. Although in practice the fluid is usually a mixture of water, methanol (antifreeze/anti-knock) and a little bit of oil to prevent corrosion. In the era of high-power aircraft piston engines it was often used to temporarily give a significant power boost. At a guess I'd say that the extra complexity (and thus cost) involved in building these engines, as well as the extra logistics (another tank to fill), has prevented it from becoming popular in mainstream use.

For petrolheads, here's an interesting story how to take a 1700 HP Rolls-Royce Merlin to 3800 HP.

You might try asking the local repair shops where/if there are any places to buy ethanol free gasoline. We had to go to another town for parts for a riding mower and the repair staff were able to point us in the right direction. They were also able to tell us which ethanol free station was better for the money.

Storage tanks do develop leaks that allow water/moisture in without leaking fuel out. If your entire area (town) also has high water tables it is entirely possible that the tank is allowing moisture in - esp. as ethanol attracts water molecules. Our repair man had his own theories about which gas station owners had bad tanks based talking to the owners of the machines he repaired or sold parts to. You might also check with the state to see if there have been any complaints against the local stations about false advertising.

I remembered doing a test for alcohol in your gasoline during an Agriculture class in college. If you take a volume of suspect gasoline (90 ml) and mix in a known quantity of water (10ml), the water will combine with any alcohol. For example, if it is pure gasoline, you would see 10ml of water settle to the bottom. If you have more than 10ml of water settle to the bottom, that shows you how much alcohol was in the gasoline. For example, if you see 18ml, that means you had your 10ml of water plus 8ml of alcohol that combined with your water.

Here is a good link with photos to demonstrate: http://www.mytractorforum.com/showthread.php?t=146217