The approximate CO2 per litre of diesel fuel is 2.68kg, and for petrol it is approximately 2.31kg. LPG produces around 1.51kg per litre.
There is not much variation in this, even with new vs old vehicles; the main factor that changes it is any unburnt fuel passing through the engine.
Choosing vehicles that produce less CO2
The more economical your vehicle, the less CO2 it produces per kilometre. Economical cars tend to have a fuel economy between 4-6 litres per 100km, while an articulated truck might use 30 litres per 100km.
- Auto stop/start: Systems that automatically stop the engine when the vehicle is stationary reduce fuel wasted through idling, which can be up to two litres an hour in a large car, a litre an hour in a small car, and a minimum of two litres an hour in a large truck (but much more when the engine is cold).
- PHEV (petrol + electric) and pure electric vehicles have lower emissions: The electric motor is used to save fuel when possible, e.g at low speeds, when stationary and when coasting. Energy can be reclaimed from braking.
- Smaller turbocharged or twin-charged (turbo+supercharger) usually offer better economy than larger engines: this depends on a few factors, but frequently the performance of a 1.4-litre twin-charged engine can be equal or better than a 2.5-litre naturally aspirated engine and tends to be more economical. However, if you are towing, then a larger engine with more torque might be a better choice.
- Choose lighter and more aerodynamic vehicles: less weight means less energy required to get it moving, and better aerodynamics means less wind resistance to keep it moving.
As the most fuel is burned during the first 10 minutes of a trip while the engine is warming up, it pays to try to combine several short trips into one longer one to minimise fuel usage.
You can calculate your fuel economy here.
Using a plug-in vehicle means that it can be charged during off-peak hours. If you have solar power to trickle charge the vehicle then the CO2 use per kilometre will be very low.