Plug-In Hybrids Emit Six Times Their Official CO2. Carmakers Want the Fix Cancelled.

Plug-in hybrids registered in the EU in 2024 emit an average of 145 g of CO2 per kilometre in real-world driving, against the 24 g/km their official type-approval figures claim. That is six times the paper number, and the gap is getting wider, not narrower.

The figures come from the European Environment Agency, which collects real-world fuel consumption from the monitors fitted to every new car sold in the EU. This dataset covers 220,000 plug-in hybrids. Transport & Environment published the analysis in September 2026.

The gap is widening

The direction of travel is the finding, not the size of the gap:

Real-world emissions rose 5% between the two years while the official figures fell 15%. The two numbers moved in opposite directions, which is why one year's five-fold gap became the next year's six-fold one.

The comparison that matters for buyers is against a petrol or diesel car, which averaged 169 g/km in real-world use in 2024. On that basis a plug-in hybrid emits 14% less than a combustion car — down from a 17% advantage the year before. Not zero, but nothing like the 86% reduction the official ratings imply.

What carmakers are asking for

The mechanism behind the discrepancy is the "utility factor": the assumption, baked into the test, about what share of a plug-in hybrid's kilometres are driven on electricity. Set it too high and the car's official CO2 figure comes out close to zero regardless of whether owners plug in. The EU legislated corrections to that factor in two stages, 2025 and 2027, to bring the assumption closer to observed behaviour.

Through ACEA, their trade body, carmakers are now pushing to have the 2027 correction cancelled. That request sits inside the ongoing revision of the EU's car CO2 standards. T&E's characterisation is that plug-in hybrids "falsely count toward climate targets" and that manufacturers are "rewarded on paper for cars that pollute almost as much as combustion cars".

Why a European Tesla buyer should care

Because the utility factor is one of the inputs that decides how many electric cars other manufacturers actually need to sell.

A fleet-average CO2 target is arithmetic. A plug-in hybrid rated at 24 g/km pulls a maker's average down almost as effectively as a battery car does, at a fraction of the engineering and pricing effort. Correct the utility factor and that same car is rated far higher, the average rises, and the shortfall has to be closed with real electric volume — cheaper electric models, or CO2 pooling bought from a maker with credits to spare.

That pooling market is one Tesla sells into, and it moves on exactly these rules: Porsche left Volkswagen's CO2 pool for XPeng's in August rather than Tesla's. Cancelling the 2027 correction would reduce the compliance pressure that creates demand for those credits and for competitively-priced EVs. Keeping it does the opposite.

Nothing changes for a European Tesla owner's car. What is being decided is how hard Tesla's competitors have to work to match it, and how much the option of not bothering costs them.

What happens next

The correction is legislated but not yet applied, and the CO2 standards revision is where it will be settled. The EEA will publish another year of monitor data, and on the trend of the last two years there is no reason to expect the gap to close on its own.