[from occupied ga]

Increase weight by adding oxygen. C=12 H=1 O=16. Use octane as the formula for gas. A gallon of gas weights 7 lb so it’s 83% carbon or 5.8 lb C. Each 12 pounds of carbon theoretically adds two oxygen or 32 lb. so a gallon of gas adds 15.4 lb O for about 20 lb.

Did y’all skip chemistry in high school?

[Henchster]

Increase weight by adding oxygen. C=12 H=1 O=16. Use octane as the formula for gas. A gallon of gas weights 7 lb so it’s 83% carbon or 5.8 lb C. Each 12 pounds of carbon theoretically adds two oxygen or 32 lb. so a gallon of gas adds 15.4 lb O for about 20 lb.

I went a different route. Average fuel/air ratio in combustion process is about 1 part fuel, 13 parts air by weight. Atmosphere = 21% Oxygen. .21 x 13 = 2.73.
Gasoline weight 6.073 pounds per U.S. gallon, times 89 octane - 5.4 pounds of combustion fuel.
Since modern engines burn very efficiently, I just went 100% burn and came up with (1 fuel unit + 2.73 oxygen units) x 5.4 pounds to get 20.142 pounds of C.