[KarlInOhio]

A gallon of gasoline weighs approximately 6 pounds.

So how do they reckon it gives off a more than 3X higher volume of waste than the initial product?

One molecule of CO2 weighs 3.66 times as much as its constituent carbon atom (12+2*16)/12.

If gasoline is pure octane (C8H18) it is 84% carbon, or about 5.3 pounds of carbon per gallon of gas which will produce 19.4 pounds per gallon. Play around with the mixture of hydrocarbon atoms and you'll get slightly different weights of CO2 produced.

[marktwain]

You did it better and faster than I did.

Congrats!