Exactly how does the EPA say "Burning one gallon of gasoline emits 20 pounds of carbon dioxide" 1 gal = 8lbs

Question

one gallon of gas weighs 8 pounds. assuming it produses no other byproducts and absorbs 100 percent its weight in O2 then thats still only 16 pounds. but we know this does not happen. i think they are blowhards trying to stretch just a little more from the thieving fuel prices

Answer 1

Gasoline is mostly carbon. When burned, it combines with oxygen to form CO2 and H20.  The carbon in the gasoline is converted almost entirely into CO2. Carbon and Oxygen have nearly the same molecular weight. Eight pounds of carbon requires about sixteen pounds of oxygen to form about 24 pounds of CO2.