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Plug-in hybrid cars emit nearly five times more planet-heating pollution than lab-reported data show, as per a new analysis.

Growing Discrepancy Between Lab and Actual Emissions

Data reveals that PHEVs release just 19% lower CO₂ than conventional petrol and diesel cars, according to analysis conducted by a non-profit organization. This differs sharply with laboratory tests, which assumed a three-quarters decrease in pollution.

Analysts studied data from onboard fuel consumption meters of 800,000 cars sold in the EU from 2021 and 2023. They found that real-world CO₂ output from PHEVs in 2023 were nearly five times greater than official figures, up from three and a half times in 2021.

“Actual CO2 output are increasing, while lab-reported figures are decreasing,” said a senior researcher involved in the report. “This gap is growing and poses a significant problem. Consequently, PHEVs pollute nearly as much as gasoline cars.”

Key Factors Driving the Emissions Gap

Researchers attributed the majority of the difference to inflated estimates of the “utility factor” – the percentage of miles driven in battery power relative to overall mileage. The team found that only a quarter of travel was completed in EV mode, whereas lab assumptions assumed over four-fifths.

Even, when running in EV mode, pollution amounts were significantly higher than lab projections. This occurred because electric motors were not strong enough to operate alone, leading to engines using gasoline for almost one-third of the travel covered in electric mode.

Regulatory and Economic Implications

According to estimates, the lowballing of PHEV CO2 output allowed four large automaker groups to escape over €5bn in penalties between 2021 and 2023, by falsely easing compliance with European Union average fleet CO₂ targets.

Additionally, owners of PHEVs would spend about €500 more annually in operating costs than would be estimated under laboratory conditions.

“The bold claims that manufacturers often promote about their plug-in hybrid cars are obviously far from the truth,” stated a transport analyst. “Buyers are being misled into thinking that by purchasing a PHEV, they are benefiting the planet and cutting money. Actually, PHEVs are little better than regular gas and diesel cars in terms of fuel consumption, CO₂ emissions, and operating costs.”

Political Discussion and Industry Pressure

Hybrid cars have recently been brought again into policy discussions as carmakers have lobbied the EU to relax CO₂ standards. A planned ban on sales of new combustion engine cars in 2035 has faced heavy lobbying from the car industry and resistance from member states with significant automotive manufacturing.

Some high-level officials have suggested PHEVs as a potential “compromise” option to introduce in the regulation.

One external energy policy specialist, who was unaffiliated with the research, called the report a “highly valuable contribution” after a long period in which parts of the automotive sector claimed there was insufficient information to properly evaluate real-world emissions.

“The results show, beyond any doubt, that the gap between official and real-world PHEV energy use and CO₂ output is much, much larger than for petrol or diesel cars,” they said. “Any policy changes concerning PHEVs should be implemented with extreme care and considering this evidence.”