You all have very interesting theories and I'm sure they are all correct in one way or another.
But there is one thing that is a variable everywhere you go that no one has mentioned.
The fuel.
There are very few federal quality control guidlines for the composition of automotive gasoline. So the quality of the fuel suffers in both composition and level of contaminates suspended in the fuel. The quality of the distilate as a fuel also depends on the crude oil's origin and the refinery that produced it. The crude oil from one area of te world is different than the oil from another area and will yeild a slightly different fuel, so refineries import crude stock from several points of origin to help maintain a higher level of consistency in their product. But still, consistency from each of the refineries is differnt and you can notice it in the way it performs in your viehicle.
There are 2 major methods of refining gasoline, distilation and fractionalization. The distilation is just like the distiling process used to make drinking alcohol. Distilation yeilds the purest fuels, however, this process on average only yeilds a specific ammount of each of these chemicals from a given ammount of crude and is rather expensive compared to fractionalization through which the refinery can control, somewhat, the ammount of any one of the distilates removed from the crude. Although less expensive this process yeilds a product lower in purity than distilation and with differnt burn characteristicts.
In some states the gasoline is mixed with some kind of alcohol such as methanol or ethanol to help reduce emissions. The problem lies in the fact that alcohols, although they burn very clean, do not have the same energy content as gasoline, so with reduced energy content per unit of measure the engine will generate less power for each unit of measure consumed.
Other states use a chemical known as MTBE (Methyl Tertiary Butyl Ether) Which has similar characteristicts as gasoline and helps the fuel burn cleaner but is toxic and has been linked to ground water pollution. This chemical also has the same effect on power output of the engine as alcohols.
Still other states have no guidelines for making blended fuels so straight gasoline is used, this will generate the highest power output.
