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Plug-in hybrid electric vehicles emit nearly 5x more planet-heating pollution than official figures indicate, according to a new analysis.

Widening Gap In Official and Actual Emissions

Data reveals that PHEVs emit just 19% less CO₂ than traditional gas and diesel vehicles, based on research carried out by a advocacy group. That differs sharply with laboratory estimates, which assumed a three-quarters decrease in emissions.

Researchers examined data from in-vehicle energy use monitors of eight hundred thousand cars registered in the EU from 2021 and 2023. They discovered that actual CO₂ output from PHEVs in 2023 were nearly five times higher than official figures, increased from 3.5 times in 2021.

“Real-world CO2 output are rising, while lab-reported figures are falling,” stated a senior researcher involved in the study. “That discrepancy is widening and poses a serious problem. As a result, PHEVs emit nearly as heavily as petrol vehicles.”

Key Factors Driving the Discrepancy

Researchers attributed most of the difference to overestimates of the “electric driving share” – the ratio of kilometers driven in electric power relative to total distance. The team determined that only a quarter of driving was done in EV mode, whereas official assumptions suggested 84%.

Even, when operating in electric mode, emission amounts were well above lab projections. This happened because electric motors were not strong sufficient to function alone, leading to engines using fossil fuels for almost a third of the travel covered in electric mode.

Regulatory and Economic Consequences

According to calculations, the underestimation of PHEV emissions allowed four major automaker groups to avoid more than €5bn in penalties between 2021 and 2023, by falsely easing compliance with EU average fleet CO₂ targets.

Additionally, owners of PHEVs would spend approximately €500 extra per year in running expenses than is assumed under laboratory conditions.

“The strong claims that manufacturers often promote about their plug-in hybrid cars are clearly far from the mark,” commented a transport analyst. “Buyers are being duped into thinking that by purchasing a PHEV, they are helping the planet and saving money. Actually, PHEVs are only slightly better than standard gas and diesel vehicles in terms of fuel consumption, CO₂ production, and running expenses.”

Political Debate and Automotive Lobbying

Hybrid cars have recently been drawn back into political discussions as carmakers have pressed the European Union to weaken CO₂ standards. A planned ban on new combustion engine vehicles in 2035 has faced heavy pressure from the automotive industry and resistance from member states with large automotive manufacturing.

Several high-level politicians have suggested PHEVs as a potential “compromise” option to include in the legislation.

An external energy policy specialist, who was unaffiliated with the research, called the analysis a “very useful contribution” after a long period in which parts of the automotive industry argued there was insufficient data to properly evaluate real-world emissions.

“The results show, without question, that the difference in lab and actual PHEV fuel consumption and CO₂ emissions is significantly greater than for petrol or conventional cars,” they said. “All regulatory adjustments regarding PHEVs should be made with extreme care and in the light of that data.”