One gallon of gasoline (6.3 lbs.) produces about 20 lbs. of carbon dioxide. This may seem weird and untrue, however, most of that weight comes from the oxygen in the air. Following the math on this means that we multiply 17.2 gallons of gas by 20 lbs. of co2 per gallon of gas burned.
This gives us the answer of 344 lbs. of carbon dioxide burned per tank of gas. (From a 2013 Honda Accord)