How Much Carbon Dioxide does a Car Produce?

The numerical carbon-hydrogen ratio in gasoline is about 8:18. Carbon weighs 12 times as much as hydrogen, so the mass fraction is 8*12:18 or 96:18, in other words carbon is about 80% of the mass of gasoline. Each carbon atom combines with two oxygen atoms to form CO2, so the mass of CO2 going out the tail pipe is 0.8*44/12 = 2.9 times the mass of gasoline going in.