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Plug-in hybrid electric vehicles produce nearly five times greater planet-heating pollution than official figures indicate, according to a new analysis.

Widening Discrepancy Between Official and Actual Emissions

Statistics reveals that PHEVs emit just 19% less CO₂ than conventional petrol and diesel vehicles, according to research carried out by a non-profit group. This differs sharply with laboratory estimates, which assumed a 75% decrease in emissions.

Researchers studied information from onboard energy use monitors of 800,000 cars sold in the EU from 2021 and 2023. They found that real-world CO₂ output from PHEVs in 2023 were 4.9 times higher than official estimates, up from three and a half times in 2021.

“Actual CO2 output are rising, while official figures are falling,” said a lead analyst participating in the study. “That gap is growing and creates a serious problem. As a result, PHEVs pollute nearly as much as petrol cars.”

Key Factors Driving the Emissions Gap

Analysts linked the majority of the gap to inflated estimates of the “utility factor” – the percentage of kilometers driven in electric mode compared to total distance. The team found that just 27% of travel was completed in electric mode, whereas lab assumptions suggested over four-fifths.

Even, when running in EV mode, emission amounts were significantly higher than lab projections. This occurred because electric motors were not strong enough to function alone, leading to combustion motors burning fossil fuels for almost one-third of the distance completed in electric mode.

Policy and Financial Consequences

According to estimates, the lowballing of PHEV CO2 output allowed several major carmaker companies to avoid more than €5bn in penalties between 2021 and 2023, by falsely simplifying adherence with European Union fleet-average CO₂ standards.

Furthermore, owners of PHEVs could pay approximately €500 more annually in running expenses than is assumed under laboratory tests.

“The strong claims that manufacturers often promote about their plug-in hybrid vehicles are obviously way off the truth,” commented a transport expert. “Consumers are being misled into believing that by purchasing a PHEV, they are benefiting the environment and cutting money. In reality, PHEVs are only slightly improved than regular petrol and diesel vehicles in terms of fuel consumption, CO₂ emissions, and operating expenses.”

Political Debate and Industry Pressure

Plug-in hybrid vehicles have lately been brought back into policy discussions as automakers have pressed the EU to relax CO₂ standards. A proposed prohibition on sales of new internal combustion vehicles in 2035 has faced heavy lobbying from the automotive sector and opposition from member states with significant car industries.

Several senior officials have suggested PHEVs as a potential “compromise” option to include in the regulation.

One external energy policy expert, who was not involved with the research, called the report a “highly valuable contribution” after years in which parts of the car sector argued there was insufficient data to accurately assess real-world emissions.

“The results demonstrate, beyond any doubt, that the difference between lab and actual PHEV energy use and CO₂ output is significantly larger than for petrol or conventional vehicles,” the expert said. “Any policy changes regarding PHEVs should be made with utmost caution and in the light of this data.”