There is 22.38 pounds of CO2 produced from burning one Gallon of Diesel Fuel.
"The US Energy Information Administration (EIA) estimated1 that U.S. gasoline and diesel fuel consumption for transportation in 2013 generated 1,095 million metric tons of CO2 from gasoline and 427 million metric tons of CO2 from diesel fuel respectively, for a total of 1,522 million metric tons of CO2.
This total was equivalent to 83% of total CO2 emissions by the U.S. transportation sector and 28% of total U.S. energy-related CO2 emissions."
How can a gallon of diesel, which weights a little over 7 pounds, be responsible for over 22 pounds of CO2? The short answer is chemistry. Diesel is hydrocarbon. That means it is composed of carbon atoms in covalent bonds with hydrogen atoms. The formula for diesel fuel is commonly known to be C12H23. When combustion occurs, the hydrogen is liberated and the carbon atoms are bonded to oxygen. Oxygen is 16 times (roughly) heavier than hydrogen. Hence, the C02 molecules have a greater mass than one might expect.