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Plug-in hybrid cars produce nearly 5x more planet-heating pollution than lab-reported figures show, according to a new report.

Growing Gap Between Lab and Real-World CO2 Output

Data shows that PHEVs release just 19% lower CO₂ than conventional petrol and diesel cars, based on research carried out by a non-profit organization. That contrasts sharply with laboratory estimates, which suggested a three-quarters decrease in emissions.

Researchers studied data from in-vehicle energy use monitors of 800,000 vehicles registered in Europe from 2021 and 2023. The team discovered that actual CO₂ output from PHEVs in 2023 were nearly five times higher than lab estimates, up from three and a half times in 2021.

“Actual emissions are rising, while official emissions are falling,” stated a lead analyst participating in the report. “That gap is growing and creates a serious problem. As a result, PHEVs pollute almost as heavily as gasoline vehicles.”

Key Factors Driving the Discrepancy

Researchers attributed most of the difference to inflated estimates of the “electric driving share” – the percentage of kilometers travelled in electric mode compared to overall distance. They found that only a quarter of travel was done in EV mode, while lab assumptions suggested 84%.

Even, when running in electric mode, emission amounts were well above lab estimates. That happened because electric motors were not strong sufficient to function independently, leading to combustion motors burning gasoline for nearly a third of the distance completed in electric mode.

Regulatory and Economic Implications

Based on estimates, the lowballing of PHEV CO2 output allowed several major automaker groups to escape more than €5bn in fines between 2021 and 2023, by artificially easing compliance with European Union fleet-average CO₂ standards.

Additionally, owners of PHEVs could pay approximately €500 extra per year in running costs than is estimated under laboratory tests.

“The strong claims that automakers like to make about their plug-in hybrid cars are clearly far from the truth,” stated a automotive expert. “Consumers are being misled into thinking that by buying a PHEV, they are benefiting the planet and saving money. Actually, PHEVs are little improved than standard petrol and diesel vehicles in terms of fuel use, CO₂ emissions, and running costs.”

Political Debate and Industry Lobbying

Plug-in hybrid cars have recently been drawn again into policy debates as automakers have lobbied the European Union to relax CO₂ standards. A proposed prohibition on sales of new combustion engine vehicles in 2035 has faced heavy lobbying from the automotive industry and resistance from member states with significant car manufacturing.

Several senior officials have suggested plug-in hybrids as a potential “flexibility” option to include in the legislation.

An external energy policy specialist, who was unaffiliated with the study, described the analysis a “highly valuable addition” after years in which segments of the car sector claimed there was too little data to properly assess real-world emissions.

“The results show, beyond any doubt, that the difference in official and real-world PHEV fuel consumption and CO₂ emissions is much, much larger than for petrol or conventional cars,” they stated. “Any policy adjustments concerning PHEVs should be made with extreme caution and in the light of this data.”