+1 Some of the higher octane fuels actually contain less energy because of additives.

 

A friend of mine, who used to work at a gas station, told me that all gasoline carried in those tanker trucks is 87 octane. They fill all of the station's tanks with 87 octane. When the guy is done pumping, he adds chemicals to the 89 octane and 93 octane tanks to change the octane rating of those gasolines.

Something to think about.