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Plug-in hybrid electric vehicles emit almost five times greater planet-heating pollution than lab-reported figures indicate, according to a new analysis.

Growing Gap Between Lab and Actual CO2 Output

Data reveals that PHEVs release only one-fifth less CO₂ than traditional gas and diesel vehicles, according to research carried out by a non-profit organization. That differs sharply with lab tests, which assumed a three-quarters reduction in emissions.

Researchers examined data from onboard fuel consumption monitors of eight hundred thousand cars sold in Europe between 2021 and 2023. They found that real-world CO₂ emissions from PHEVs in 2023 were nearly five times higher than lab figures, up from three and a half times in 2021.

“Actual CO2 output are rising, while lab-reported emissions are falling,” said a lead researcher involved in the report. “That gap is growing and poses a serious issue. As a result, PHEVs pollute almost as heavily as petrol cars.”

Key Reasons Driving the Discrepancy

Researchers linked most of the difference to inflated estimates of the “utility factor” – the ratio of kilometers driven in electric mode compared to overall distance. The team found that just a quarter of travel was done in electric mode, while official assumptions suggested 84%.

Even, when operating in electric mode, emission amounts were significantly higher than official estimates. This occurred because electric motors were not strong sufficient to function alone, resulting to engines burning fossil fuels for nearly a third of the distance completed in electric mode.

Regulatory and Financial Consequences

According to calculations, the underestimation of PHEV CO2 output allowed four major carmaker groups to escape over €5bn in fines from 2021 and 2023, by artificially simplifying compliance with European Union average fleet CO₂ standards.

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

“The strong claims that automakers often promote about their PHEV cars are clearly far from the truth,” commented a transport expert. “Consumers are being duped into believing that by buying a PHEV, they are benefiting the planet and saving costs. Actually, PHEVs are only slightly improved than standard gas and diesel vehicles in terms of fuel consumption, CO₂ emissions, and operating expenses.”

Policy Debate and Industry Pressure

Plug-in hybrid cars have lately been drawn back into political debates as carmakers have lobbied the EU to weaken CO₂ standards. A planned prohibition on sales of new internal combustion cars in 2035 has faced intense pressure from the automotive industry and resistance from EU countries with large car manufacturing.

Several senior politicians have suggested plug-in hybrids as a potential “compromise” solution to introduce in the regulation.

One independent energy policy specialist, who was not involved with the research, described the report a “very useful contribution” after years in which parts of the car sector argued there was too little data to properly evaluate actual CO2 output.

“The results demonstrate, without question, that the gap in official and actual PHEV fuel consumption and CO₂ emissions is significantly greater than for gasoline or diesel cars,” the expert stated. “Any policy adjustments regarding PHEVs should be implemented with extreme caution and considering this evidence.”