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PHEVs release nearly 5x more planet-heating pollution than official data show, according to a new report.

Growing Gap Between Lab and Real-World Emissions

Data shows that PHEVs release only 19% less CO₂ than traditional gas and diesel vehicles, according to research conducted by a non-profit group. This contrasts sharply with laboratory tests, which assumed a 75% decrease in pollution.

Analysts examined data from onboard fuel consumption monitors of eight hundred thousand cars registered in the EU between 2021 and 2023. They discovered that actual CO₂ output from PHEVs in 2023 were 4.9 times higher than official figures, increased from 3.5 times in 2021.

“Actual CO2 output are rising, while official figures are decreasing,” said a senior researcher participating in the study. “That discrepancy is widening and poses a serious issue. Consequently, PHEVs pollute almost as much as petrol cars.”

Primary Reasons Behind the Emissions Gap

Researchers attributed the majority of the difference to overestimates of the “electric driving share” – the percentage of miles travelled in battery mode relative to overall mileage. The team determined that only 27% of travel was completed in electric mode, while lab estimates assumed over four-fifths.

Even, when operating in EV mode, emission levels were significantly higher than lab estimates. That occurred because EV motors were not strong enough to function alone, resulting to engines using gasoline for almost a third of the travel completed in electric mode.

Policy and Economic Consequences

According to estimates, the underestimation of PHEV emissions allowed several large carmaker groups to escape over €5bn in fines from 2021 and 2023, by falsely simplifying adherence with EU average fleet CO₂ standards.

Additionally, drivers of PHEVs could spend approximately €500 extra per year in running costs than is estimated under lab tests.

“The bold statements that manufacturers like to make about their plug-in hybrid cars are clearly far from the truth,” stated a transport expert. “Buyers are being duped into believing that by purchasing a PHEV, they are benefiting the planet and cutting costs. Actually, PHEVs are only slightly improved than regular gas and diesel vehicles in terms of energy consumption, CO₂ production, and running expenses.”

Policy Discussion and Industry Pressure

Plug-in hybrid cars have recently been brought back into policy discussions as carmakers have lobbied the EU to weaken CO₂ standards. A planned prohibition on new combustion engine vehicles in 2035 has faced intense lobbying from the car industry and opposition from member states with significant car manufacturing.

Several senior politicians have suggested plug-in hybrids as a potential “compromise” solution to include in the legislation.

One external energy economics expert, who was not involved with the research, called the analysis a “very useful contribution” after years in which parts of the automotive industry claimed there was insufficient data to accurately evaluate actual emissions.

“These findings show, without question, that the difference in lab and real-world PHEV fuel consumption and CO₂ emissions is much, much larger than for gasoline or diesel cars,” the expert stated. “Any regulatory adjustments concerning PHEVs should be made with extreme care and in the light of that evidence.”