Perty inneresting.
It also becomes clear how gasahol shoves it in the motorist a little deeper, as well -- radically lower btu's per gallon.
Unbeknownst to most people, regular gas has more btu's/gal than high test -- by dint of the higher stability of the tertiary carbocation intermediate, in the combustion process.... no foolin. Texaco was successfully sued over this li'l factoid, in their false advertising of their premium fuels. Someone at Texaco didn't pay attention in Organic Chem I.
#6 fuel oil has markedly higher energy per gal:
Some other useful charts: