Many of you know that I regularly debunk the claim that diesel vehicles emit less CO2 than electric vehicles. But one thing that I hadn’t really worked out is just how much CO2 is emitted when gasoline and diesel is produced. It turns out that I was far too conservative. Once you know the exhaust emissions from a car, you should add a whopping 30% for a gasoline car and 24% for a diesel!

I’ve been writing about the inevitability of electric vehicles for about fifteen years now. Sometimes people call me an evangelist and say I’m too optimistic. But my tune has never changed and I’ve always stuck to the facts. Yet one thing was a bit of a black box to me … Exactly how much CO2 is emitted during gasoline and diesel production?

So far I just took the numbers of RVO/CE-Delft/TNO1 into account without really understanding how they arrived at those figures. That went fine for many years. However, my ignorance was exposed in a recent discussion with Martien Visser and Cees vd Leun where I could not square super efficient refineries with emissions that I knew to be larger.

I started to comb through dozens of scientific sources. But man, that is hard. It cost me my entire weekend! The oil business is a world unto itself with various priorities, sources and even different units. To make matters worse, there are major differences between oil wells and refineries. And it was all very hard to read for a non-expert like me.

So, I asked for input on twitter. Turns out Jonathan Koomey (one of my friends/followers) had recently co-written an authoritative commentary in Science (version without paywall here). It manages to present a wealth of facts in just three pages but also offers another hundred pages of supplementary material if you are interested. It includes data from what must be thousands of sources and covers 98% of global oil production and also looks at things like flaring. This was one monster of an undertaking: hats off to these researchers. I consider this the new standard now. The image below summarizes what they found. The end result was that getting a barrel of oil to the refinery emits more CO2 than previously thought: a global average weighted value is around 10.3 gram CO2eq/MJ.2 (That’s 63 kg of CO2 for every barrel delivered to a refinery).

Refining and transportation

The next step is refining oil. A recent study for the EU looked at this topic in depth and estimated that refineries add 10.2 gram CO2eq/MJ for gasoline and 5.4 for diesel.3 However, refineries outside of Europe and North America have higher emissions4 and account for around half of global production5 so this is probably a conservative estimate in terms of estimating global amounts.

For Europe, transporting the stuff to a gas pump near you adds just over 1 gr CO2eq/MJ.6 It’s a small but significant addition.

In jargon we call all this stuff that needs to happen before you can pump gasoline or diesel at the gas station the well to tank (WTT) emissions factor. So, I now think the best estimates for these are as follows:

CO2 equivalent in grams of Well to Tank (WTT) emissions from gasoline and diesel:
FuelPer megajoule (MJ)Per kilowatt hour (kWh)Per litre7
Gasoline21.577720
Diesel16.760640

 

This comes on top of the 2420 gr/l for pure gasoline and 2670 gr/l for pure diesel1 that is emitted when you burn gasoline or diesel in your car.

(We are sidestepping the discussion on CO2 emissions related to biofuels by taking pure fossil fuels and not the mix you might find on the market. If gasoline and diesel including biofuels were used, the emissions would drop slightly if optimistic values where used and rise slightly when adjustments for indirect land use were to be considered. By the way, I’m not a fan of biofuels for cars and truck. A car consumes about the same as 10 humans do and a big truck about the same as 300 humans if my memory serves me correctly.)

Conclusion

When you know how much CO2 is emitted through the exhaust, you must add 30% for gasoline and 24% for diesel in order to arrive at the total amount of GHG emissions. Or, to close with another table:

Total CO2 emissions for gasoline and diesel
Gasoline3140 grams per litre
Diesel3310 grams per litre

 

References

  1. P.J. Zijlema. List of fuels and standard CO2 emission factors. https://english.rvo.nl/sites/default/files/2019/05/The%20Netherlands%20list%20of%20fuels%20version%20January%202019.pdf (2019).
  2. Masnadi, M. S. et al. Global carbon intensity of crude oil production. Science 361, 851–853 (2018).
  3. Gordillo, V., Rankovic, N. & Abdul-Manan, A. F. N. Customizing CO2 allocation using a new non-iterative method to reflect operational constraints in complex EU refineries. Int J Life Cycle Assess 23, 1527–1541 (2018).
  4. Mohammed Atris, A. Assessment of oil refinery performance: Application of data envelopment analysis-discriminant analysis. Resources Policy 65, 101543 (2020).
  5. FuelsEurope. FuelsEurope Statistical Report 2018. (2018).
  6. Edwards, R. et al. Well-to-wheels analysis of future automotive fuels and power trains in the European context report version 3c, July 2011. (Publications Office, 2011).
  7. Energy conversion calculators – U.S. Energy Information Administration (EIA). https://www.eia.gov/energyexplained/units-and-calculators/energy-conversion-calculators.php.