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Plug-in hybrid cars release almost five times greater planet-heating emissions than lab-reported data indicate, according to a new analysis.

Widening Discrepancy Between Official and Actual CO2 Output

Statistics shows that PHEVs release just 19% less CO₂ than traditional petrol and diesel vehicles, according to research carried out by a advocacy group. That differs sharply with lab estimates, which assumed a three-quarters decrease in pollution.

Researchers studied information from onboard fuel consumption monitors of 800,000 cars registered in the EU from 2021 and 2023. The team discovered that actual CO₂ emissions from PHEVs in 2023 were 4.9 times greater than official estimates, increased from three and a half times in 2021.

“Real-world emissions are rising, while official emissions are decreasing,” stated a senior analyst participating in the study. “This discrepancy is growing and creates a significant issue. Consequently, PHEVs pollute almost as heavily as gasoline cars.”

Primary Reasons Behind the Discrepancy

Analysts attributed most of the gap to inflated estimates of the “utility factor” – the percentage of kilometers driven in electric power compared to total distance. The team found that only a quarter of driving was completed in EV mode, whereas lab assumptions assumed over four-fifths.

Even, when running in EV mode, emission amounts were well above official estimates. This happened because EV motors were insufficiently powerful enough to operate alone, leading to combustion motors burning gasoline for nearly one-third of the travel completed in EV mode.

Regulatory and Financial Implications

Based on calculations, the underestimation of PHEV CO2 output allowed four large automaker groups to avoid over €5bn in fines from 2021 and 2023, by artificially easing adherence with EU average fleet CO₂ targets.

Furthermore, drivers of PHEVs could spend approximately €500 extra annually in running expenses than is assumed under lab conditions.

“The strong statements that manufacturers often promote about their plug-in hybrid cars are obviously way off the truth,” commented a transport analyst. “Consumers are being duped into believing that by purchasing a PHEV, they are benefiting the environment and cutting money. Actually, PHEVs are little improved than regular petrol and diesel cars in terms of fuel consumption, CO₂ emissions, and running costs.”

Policy Discussion and Industry Lobbying

Hybrid cars have recently been drawn again into political debates as carmakers have pressed the European Union to weaken CO₂ standards. A proposed ban on sales of new internal combustion vehicles in 2035 has faced intense lobbying from the car industry and resistance from EU countries with significant car manufacturing.

Several high-level officials have suggested PHEVs as a potential “flexibility” option to include in the legislation.

One external energy policy specialist, who was unaffiliated with the study, called the report a “highly valuable contribution” after a long period in which segments of the automotive sector argued there was too little information to properly assess real-world emissions.

“These findings demonstrate, beyond any doubt, that the gap in official and real-world PHEV fuel consumption and CO₂ emissions is significantly greater than for gasoline or diesel cars,” the expert stated. “Any regulatory changes regarding PHEVs should be implemented with extreme caution and considering that evidence.”