Plug-in hybrids consume much more fuel than stated in theory. ICCT reports a 4.6-fold difference.
Plug-in hybrids were supposed to be a smooth transition between gasoline vehicles and electric cars. Yet an ICCT analysis based on data from around 920,000 PHEV vehicles in Europe shows that their actual CO2 emissions were on average 3.5 times higher in 2021 and as much as 4.6 times higher in 2023 than those reported during homologation. By 2027, the European Union plans to improve the rules for calculating these emissions, which will hit manufacturers that currently rely heavily on PHEVs to meet fleet emission standards.
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The problem isn’t new, but its scale is becoming increasingly problematic. Especially for brands that sell plug-ins as “almost electric” cars.
The longer the electric range, the greater the discrepancies
ICCT based its analysis on OBFCM data, which is onboard fuel and energy consumption monitoring published by the European Environment Agency. These are not figures from brochures but records of actual vehicle operation from 2021-2023.
The conclusion is simple: drivers of PHEVs use electric power less often than assumed by homologation standards. Worse still, the proportion of driving in electric mode is declining, even though newer models come with larger batteries and greater electric range. It sounds absurd, but that’s how the current system works.
The EU homologation is based on the so-called utility factor, which is a curve that assumes if a car travels more kilometers on electricity, the driver will charge it more often and use electric drive more frequently. In practice, it’s often the opposite. The car has a larger battery, so on paper it performs well, but in everyday use it’s still driven like a regular hybrid with a charging port that no one uses regularly.
ICCT states outright that the greater the electric range of a PHEV, the larger the gap between official emissions and actual emissions. Not good.
Only 18 percent better than regular gasoline and hybrid cars
The most concerning part of the report relates to the overall impact. According to the analysis, actual emissions from PHEVs are only about 18 percent lower than those of conventional gasoline cars and regular hybrids without plug-in charging.
This is far too little if we remember how these cars were positioned over the years. They were supposed to deliver most of the benefits of EVs without the hassle of charging. In the lab, this worked. On the road, it doesn’t quite hold up.
The issue also has financial and regulatory dimensions. Lowered homologation emissions help manufacturers meet EU CO2 limits for fleets. In other words, PHEVs offer brands significant paper advantages today, even if they actually emit much more in reality. According to ICCT, such a system misleads consumers about energy costs and unfairly favors plug-in vehicles in taxes or incentives where such preferences still exist.
2027 could change the rules of the game
The European Commission had already identified the problem earlier. The first adjustment to the utility factor curve took effect in 2025. A second adjustment is planned for 2027, and it is this one that could trigger a more intense dispute between Brussels and manufacturers.
ICCT believes this adjustment should not be diluted or delayed. Even after the 2025 changes, the official emissions figures for PHEVs remain significantly lower than actual values. It is only the 2027 update that is expected to narrow this gap to levels seen in conventional gasoline vehicles, where there is also a discrepancy but one that is much smaller.
The organization wants one more thing: regular updates to the utility factor curve based on OBFCM data after 2027. This one does sound reasonable. If manufacturers and drivers change the way they use their vehicles, the system should keep up rather than rely on assumptions from years ago.
Against this backdrop of discussion, a market shift is also evident. Data cited in European debates show that BEV sales share in the EU rose from 15.6 percent in the first half of 2025 to 20.7 percent a year later. PHEVs saw a much more modest increase, from 8.5 percent to 9.8 percent. If 2027 takes away part of their homologation advantage, this segment could slow down even further.
Plug-in vehicles were meant to be a compromise, but they increasingly seem like a technology that works best in Excel. What do you think? Should the Union reduce preferences for PHEVs more significantly starting in 2027?
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