One gallon of carbon petroleum fuel weighing 7 pounds becomes 22 pounds of carbon dioxide. Essentially in burning fuel you replace carbon plus two hydrogen atom

One gallon of carbon petroleum fuel weighing 7 pounds becomes 22 pounds of carbon dioxide. Essentially in burning fuel you replace carbon plus two hydrogen atoms- atomic weight 14- with a carbon plus two oxygen atoms- atomic weight 44. That is an increase of 3.14x.