`CO_2 "produced" = 12.65 "lb" / "gal"`

12.65

This constant represents the approximate amount of carbon dioxide (CO₂) that is produced when you burn a gallon of propane.

Notes

"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."