RE: ethanol
This is a common lab experiment. Mix 1 unit volume of ethanol and 1 unit volume of water and mix well. Then measure the resulting volume, and it is 1.92 units of volume, not 2.0 units. This is due to the difference in size of water and ethanol molecules. Gasoline works this way too with ethanol, so you end up with a smaller volume than the volume of the two parts mixed together.
Oil companies get about 3% more volume of gasoline from a barrel of oil when they can mix in ethanol. And it is a lower octane too, since the ethanol brings it up to the standard 87 octane. Of course if you live in a mountain state, you may be buying 85 octane fuel because of the lower air pressure.