What is the CO2 emission per liter petrol?

Answer:

I think this depends on how good the engine is, since cars with similar mileage per gallon are quoted as having widely different CO2 emmission rates.

Burnt under ideal conditions the figure is very close to 2.3 kg CO2 produced per litre of petrol used. One litre of petrol weighs less than 1 kg however the additional mass comes from atmospheric O2. Differences in result are introduced by many factors including: the quality of the petrol used, how completely the petrol is burnt, the measuring technique, and in an engine the age/efficiency of the engine, etc.