[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.

[from occupied ga]

Both ways appear to work, so the people who were saying not possible apparently majored in gender studies or theater. My numbers were only meant to be approximate, and you can count on near 100% combustion because of catalytic converters