Average cost of 100LL in the U.S., April 2017: $4.75/gal. Density of avgas (all grades) at 15° C: 6.01 lbs./U.S. gal. Density of avgas (all grades) at -40° C: 6.41 lbs./U.S. gal.

How much does a gallon of airplane fuel weigh?

Unless the specific weight for an item is known, the standard weights used in aircraft weight and balance are as follows: Aviation gasoline 6 lb/gal. Turbine fuel 6.7 lb/gal.

Why is 100LL so expensive?

100LL fuel has many more “aromatic” hydrocarbons than mogas (auto fuel) in order to increase the octane levels and prevent fuel from vaporizing in your lines at high altitude. It’s much higher grade, so it costs more.

It is generally safe to operate engines with a higher octane fuel than required, but not lower. Some people have tried to use 100 octane avgas in race cars to stop premature detonation in turbocharged engines, but it requires engine modifications to perform well.