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Plug-in hybrid electric vehicles emit nearly 5x greater planet-heating pollution than lab-reported figures indicate, according to a new report.

Widening Gap Between Lab and Actual Emissions

Statistics shows that PHEVs release only one-fifth lower CO₂ than traditional petrol and diesel vehicles, based on research carried out by a non-profit organization. This differs sharply with lab tests, which suggested a three-quarters decrease in emissions.

Researchers studied information from onboard fuel consumption monitors of eight hundred thousand cars sold in Europe from 2021 and 2023. The team found that actual CO₂ emissions from PHEVs in 2023 were nearly five times higher than lab figures, up from 3.5 times in 2021.

“Real-world CO2 output are increasing, while lab-reported figures are falling,” said a lead analyst involved in the report. “That discrepancy is growing and creates a serious issue. As a result, PHEVs pollute almost as much as petrol vehicles.”

Primary Factors Driving the Emissions Gap

Researchers linked the majority of the gap to overestimates of the “utility factor” – the percentage of kilometers travelled in battery mode compared to overall distance. The team found that only a quarter of driving was done in EV mode, whereas lab assumptions assumed over four-fifths.

Additionally, when running in electric mode, pollution levels were well above lab estimates. This happened because electric motors were not strong enough to operate alone, leading to combustion motors burning fossil fuels for almost a third of the distance covered in electric mode.

Policy and Financial Implications

Based on calculations, the underestimation of PHEV CO2 output enabled several major carmaker companies to avoid over €5bn in fines from 2021 and 2023, by falsely easing adherence with EU average fleet CO₂ standards.

Additionally, drivers of PHEVs could pay about €500 extra per year in running expenses than would be assumed under lab conditions.

“The bold statements that automakers like to make about their PHEV vehicles are obviously far from the truth,” stated a automotive expert. “Buyers are being duped into believing that by purchasing a PHEV, they are helping the planet and saving money. Actually, PHEVs are only slightly improved than standard petrol and diesel cars in terms of fuel use, CO₂ production, and operating costs.”

Political Debate and Industry Lobbying

Plug-in hybrid vehicles have lately been drawn back into policy debates as automakers have lobbied the European Union to weaken CO₂ targets. A proposed ban on sales of new internal combustion cars in 2035 has faced intense pressure from the car sector and opposition from member states with significant car manufacturing.

Some senior politicians have proposed PHEVs as a possible “compromise” option to include in the regulation.

One external energy economics specialist, who was not involved with the study, described the analysis a “highly valuable addition” after a long period in which parts of the automotive sector argued there was insufficient data to properly evaluate actual emissions.

“These findings show, beyond any doubt, that the difference in official and real-world PHEV energy use and CO₂ emissions is significantly greater than for petrol or conventional vehicles,” the expert said. “Any regulatory adjustments regarding PHEVs should be implemented with extreme care and in the light of this evidence.”