Every New Car in Europe Counts Its Own Fuel. For Plug-In Hybrids the Meter Reads About Five Times the Official Figure.
Since 2021 new cars sold in the EU carry a device that records lifetime fuel use, and since May 2023 the roadworthiness test collects the reading. For cars registered in 2023 the petrol and diesel gap is 19 per cent. For plug-in hybrids it is 401 per cent.
In short
What happened. New cars sold in the European Union have carried an on-board fuel meter since 2021. Manufacturers report the readings every April, and since 20 May 2023 the roadworthiness test collects them as well.
What it means. The laboratory figure printed on a car’s papers can now be set against what the car actually burned. For petrol and diesel the difference is modest. For plug-in hybrids it is not.
Risks and impact. For cars first registered in 2023, real-world CO2 ran 19 per cent above the official value for combustion cars and 401 per cent above it for plug-in hybrids, on roughly 8 million cars of data.
What can be done. Treat a plug-in hybrid’s official CO2 as an assumption about charging habits rather than a measurement. The European Environment Agency publishes the aggregated figures.
What to watch. The assumption behind that figure is due to tighten on 29 November 2026, and a group of member states has asked for it to be frozen instead.
Shown as a summary because of your reading settings.
What happened
The device is called an OBFCM, an on-board fuel and energy consumption monitoring device. Since 2021 it has been required on new cars sold in the EU that burn liquid fuel. It keeps two running lifetime totals: fuel consumed and distance travelled. On a plug-in hybrid it also logs the fuel used in charge-depleting operation, the distance covered with the engine off, and the total grid energy that went into the battery.
Two rules move that data off the car. Under Implementing Regulation (EU) 2021/392, manufacturers report by 1 April each year, either by direct transfer from the vehicle or through dealers and repairers at each service visit. And “with effect from 20 May 2023, the real-world data together with the VINs shall be collected when the vehicles undergo roadworthiness tests”.
The result is a very large dataset. The European Environment Agency’s file for reporting year 2023 came from 54 manufacturers and 18 member states, and after cleaning it holds 2.8 million cars first registered in 2021, 2.5 million from 2022 and 1.2 million from 2023.
The Commission’s published summary of the readings gathered in 2022 found real-world CO2 from petrol and diesel cars “on average, around 20% higher than indicated by the official values”. For 320,000 plug-in hybrids registered in 2021, it found real-world emissions “on average 3.5 times (99 g CO2/km) higher than the type-approval values”. By registration year 2023, on roughly 8 million cars of data, independent analysis puts those two gaps at 19 per cent and 401 per cent.
What the evidence supports
Two findings are now supported by more than one independent analysis of the same public data.
The combustion gap is real but small and stable. Working through roughly 8 million cars registered between 2021 and 2023, the International Council on Clean Transportation put the gap for petrol and diesel cars, including mild and full hybrids, at 18, 18 and 19 per cent by registration year. Driver-reported fuel logs from a German website gave a lower figure, 11 to 12 per cent, but the same slow upward drift.
The plug-in hybrid gap is neither small nor stable: 265 per cent, 323 per cent and 401 per cent across the same three years. Transport & Environment, working separately on more than 800,000 plug-in hybrids in the same dataset, reported the ratio rising from 3.5 times in 2021 to nearly five times in 2023.
Cautions belong with those numbers. Coverage is partial and thins each year: the samples cover about 42, 33 and 13 per cent of combustion registrations and about 54, 38 and 16 per cent of plug-in hybrid registrations for 2021, 2022 and 2023. Nothing is randomly sampled, though the ICCT reports that once weighted its sample matched the registered fleet’s average test CO2 to within a gram. And a fleet average is not a forecast for any one car or driver.
Both analyses come from organisations that campaign for lower emissions; the ICCT report names the European Climate Foundation as its funder. They also work from a dataset the Commission publishes, which is the useful part.
How the story is being framed
The lab test was never a promise about your fuel bill. It exists so two cars can be compared on identical terms, and for combustion cars it does that tolerably. The objection holds until the comparison starts to depend on an assumption about the owner rather than a measurement of the machine.
People simply do not plug them in. Company cars, fuel cards, no charger at home, and a full tank is faster than a full battery. The meter data says this is largely true. What it leaves out is that nobody asked drivers what they would do; the regulation assumed it, and the assumption became the number that counted.
Fix the assumption. That is the Commission’s route, and it is already under way. Transport & Environment’s own estimate is that even after the second correction the average real-world gap for plug-in hybrids would still be about 18 per cent. Narrower, not closed.
Or freeze it. The Council’s progress report of 15 June 2026 records the fight in one sentence: “a group of delegations have called for freezing the so called ‘utility factor’ for plug-in hybrid vehicles, while another group opposes this.” Manufacturers count these cars towards their fleet targets at the official figure, which is what makes a scaling parameter worth arguing about.
The background
Here is how a plug-in hybrid’s official number is built, because almost nobody is told. The car is tested twice: once starting from a full battery, once with the battery empty. The two results are blended, and the weighting is a single value called the utility factor — the share of driving the regulation assumes will happen on the electric side. It is not measured. It is read off a curve as a function of the car’s electric range.
That curve has been redrawn. Recital 18 of Commission Regulation (EU) 2023/443 says why, in the flattest possible language: studies show a significant difference between real-world and test CO2 for these cars, so “the utility factors applied for the purpose of the CO2 emission determination at type approval should be revised”, first on available data and then again using the fuel-meter readings. Transport & Environment’s reading of the successive curves: for a car with 60 kilometres of electric range, the assumed electric share falls from over 80 per cent to 54 per cent, and to 34 per cent after the second step. The Council report says the second step applies from 29 November 2026.
The effect of the old assumption shows up in the fleet numbers. Official average CO2 for new cars fell 28 per cent between 2018 and 2023; the ICCT’s estimate of the real-world average fell 15 per cent, and that reduction came from battery-electric sales rather than from cleaner combustion. Article 12 of Regulation (EU) 2019/631 sets one more deadline: by 31 December 2026 the Commission must publish a methodology for adjusting each manufacturer’s average CO2 from 2030 using real-world data.
The deeper story
Most official numbers on a car describe the car. Kerb weight, boot volume, power. The CO2 figure for a plug-in hybrid is a different kind of thing: it describes the car twice and then makes a prediction about the person who will own it.
That is not a scandal in itself. Anything sold as usable has an assumption about use baked into it, and someone has to write the assumption down. What is unusual here is that the assumption was worth money. Every point of assumed electric driving lowered the official figure, and the official figure counted against a manufacturer’s fleet target. Nobody had to lie. The generous guess was simply left in place while the market rearranged itself around it.
The genuinely interesting move came from the same body of rules. A 2018 amendment required the instrument; the 2019 standards required it to report. Between them they built the thing that would eventually contradict the assumption: a meter, in every car, filed annually, and read again at the roadworthiness test. That is a rare thing for an institution to do — to write the audit into the rule it is about to be judged by, knowing it will take years to speak and will flatter nobody when it does.
It took five years. Meters fitted in 2021, first Commission report in 2024, the curve moving in November 2026, and the mechanism for docking manufacturers who drift still homework due at the end of this year. Slow. But that is what a self-correcting rule looks like from the inside, and the alternative is a number nobody can check at all.
Which leaves the ordinary question. On the papers of the next car you look at, how much of the figure is a measurement, and how much is a guess about you?
Something to sit with
If an official figure quietly assumes something about your habits, would you rather it assumed the best of you or the average of everyone?
Where else does a rule contain the instrument that could prove it wrong, and who is expected to look at the readings?
Sources
- Regulation (EU) 2019/631, Article 12 (real-world CO2 emissions and fuel consumption data), consolidated text of 1 January 2025 — https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:0201...
- Commission Implementing Regulation (EU) 2021/392, Articles 9 and 10 (monitoring and reporting of CO2 emissions from passenger cars and light commercial vehicles) — https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:32021R0392
- Commission Regulation (EU) 2018/1832, Annex X (devices for monitoring the consumption of fuel and electric energy) — https://www.legislation.gov.uk/eur/2018/1832/annex/X?view=plain
- Commission Regulation (EU) 2023/443, recital 18 (revision of the utility factors for plug-in hybrids) — https://eur-lex.europa.eu/eli/reg/2023/443/oj/eng
- European Commission — report on real-world CO2 emissions and fuel consumption of new cars and vans, COM(2024) 122 final — https://climate.ec.europa.eu/document/download/b644dafe-1385-4b56-9...
- European Commission — publication of real-world CO2 emissions and fuel consumption of cars and vans collected in 2022 — https://climate.ec.europa.eu/news-other-reads/news/publication-real...
- European Environment Agency — real-world emissions, scope and coverage of the OBFCM dataset for reporting year 2023 — https://climate-energy.eea.europa.eu/topics/transport/real-world-em...
- Council of the European Union — progress report on the CO2 standards proposal, document 10065/1/26 REV 1, interinstitutional file 2025/0420 (COD) — https://data.consilium.europa.eu/doc/document/ST-10065-2026-REV-1/en/pdf
- International Council on Clean Transportation — On the way to real-world CO2 values? Evidence from 2021-2023 on-board fuel consumption monitoring data — https://theicct.org/wp-content/uploads/2026/06/ID-627-%E2%80%93-Rea...
- Transport & Environment — Closing the growing PHEV loophole, briefing on the utility factor correction — https://uploads.transportenvironment.org/production/files/2025_09_T...
- Oeko-Institut and ifeu — Regulatory adjustments for plug-in hybrid vehicles in Europe — https://www.oeko.de/fileadmin/oekodoc/Analyse_PHEV_2025_EN_final.pdf
- European Parliamentary Research Service — Revision of CO2 emission performance standards for new light-duty vehicles and vehicle labelling, PE 782.664 — https://www.europarl.europa.eu/RegData/etudes/BRIE/2026/782664/EPRS...
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