How much energy is released by burning Petrol?

Burning one litre of Petrol releases 2.36 kg of CO2 (under the 'perfect' fuel/air mixture). I know this sounds unreasonable when one litre of petrol weighs around 0.75 kg, but the majority (over 70%) of the CO2 weight is made up of the oxygen which is consumed from the air and does not originate from the petrol.