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

Widening Gap Between Lab and Actual CO2 Output

Data shows that PHEVs release only 19% less CO₂ than conventional gas and diesel vehicles, based on analysis conducted by a non-profit organization. That contrasts significantly with lab tests, which suggested a three-quarters reduction in emissions.

Researchers examined data from in-vehicle fuel consumption meters of 800,000 vehicles sold in the EU between 2021 and 2023. The team found that real-world CO₂ emissions from PHEVs in 2023 were nearly five times higher than official figures, increased from 3.5 times in 2021.

“Actual emissions are increasing, while official figures are decreasing,” said a lead researcher participating in the study. “This gap is growing and creates a significant issue. As a result, PHEVs pollute almost as much as gasoline cars.”

Primary Factors Driving the Discrepancy

Researchers linked the majority of the difference to inflated estimates of the “electric driving share” – the ratio of miles driven in battery mode compared to overall distance. They determined that just 27% of travel was done in electric mode, whereas lab estimates suggested over four-fifths.

Even, when running in electric mode, pollution levels were significantly higher than lab projections. This happened because electric motors were not strong enough to function alone, resulting to engines using gasoline for nearly one-third of the travel covered in electric mode.

Regulatory and Economic Consequences

Based on calculations, the lowballing of PHEV emissions allowed four large automaker groups to avoid more than €5bn in fines from 2021 and 2023, by artificially easing compliance with European Union average fleet CO₂ targets.

Additionally, owners of PHEVs could spend approximately €500 more annually in operating costs than would be estimated under lab tests.

“The strong statements that automakers like to make about their PHEV vehicles are obviously far from the truth,” commented a transport analyst. “Buyers are being duped into believing that by buying a PHEV, they are helping the planet and saving costs. Actually, PHEVs are little better than regular petrol and diesel vehicles in terms of fuel use, CO₂ emissions, and running costs.”

Policy Debate and Industry Lobbying

Plug-in hybrid vehicles have recently been drawn again into political debates as automakers have lobbied the European Union to relax CO₂ targets. A proposed ban on new combustion engine cars in 2035 has faced intense lobbying from the car industry and resistance from EU countries with large car manufacturing.

Some high-level officials have proposed PHEVs as a possible “compromise” solution to introduce in the regulation.

An independent energy policy expert, who was unaffiliated with the study, called the report a “very useful addition” after years in which parts of the automotive sector claimed there was insufficient data to accurately assess actual CO2 output.

“These findings demonstrate, beyond any doubt, that the gap in lab and real-world PHEV energy use and CO₂ output is significantly greater than for petrol or diesel cars,” the expert said. “All regulatory changes concerning PHEVs should be implemented with utmost caution and in the light of this evidence.”