Burning 1 gallon of gasoline creates 20 pounds of equivalent CO2. Fossil fuel-powered transportation pumps more than 1.7 billion tons of carbon equivalent emissions into the air annually.

It seems impossible that a gallon of gasoline, which weighs about 6.3 pounds, could produce 20 pounds of carbon dioxide (CO2) when burned. However, most of the weight of the CO2 doesn't come from the gasoline itself, but the oxygen in the air. When gasoline burns, the carbon and hydrogen separate. The hydrogen combines with oxygen to form water (H2O), and carbon combines with oxygen to form carbon dioxide (CO2).

Each of those cars, on average, produces 20 pounds of carbon dioxide for every gallon of gas it consumes

Using one gallon of gasoline in your car produces about 20 pounds of carbon dioxide emissions directly, or 26 pounds if you account for upstream processing of the fuel.

About 19.64 pounds of carbon dioxide (CO2) are produced from burning a gallon of gasoline that does not contain ethanol. Most of the retail gasoline now sold in the U.S. contains about 10% ethanol by volume.  Under international agreement, CO2 from ethanol and other biofuels are not counted at the tailpipe, so burning a gallon of gasoline with 10% ethanol produces about 17.68 pounds of CO2.