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Plug-in hybrid electric vehicles release nearly 5x greater global warming emissions than lab-reported data show, according to a new analysis.

Widening Gap Between Official and Real-World Emissions

Statistics shows that PHEVs emit only 19% less CO₂ than traditional gas and diesel vehicles, according to research conducted by a non-profit organization. That contrasts significantly with laboratory tests, which assumed a 75% decrease in pollution.

Analysts examined data from in-vehicle fuel consumption monitors of eight hundred thousand cars sold in the EU from 2021 and 2023. They found that actual CO₂ emissions from PHEVs in 2023 were nearly five times greater than official estimates, up from 3.5 times in 2021.

“Actual CO2 output are rising, while lab-reported figures are decreasing,” stated a lead researcher participating in the study. “This discrepancy is widening and poses a significant problem. As a result, PHEVs emit nearly as heavily as petrol cars.”

Key Reasons Behind the Discrepancy

Researchers attributed most of the gap to inflated estimates of the “utility factor” – the percentage of kilometers travelled in electric mode relative to total mileage. They determined that just 27% of driving was completed in EV mode, while lab assumptions assumed 84%.

Even, when running in EV mode, pollution levels were well above lab estimates. This happened because electric motors were not strong enough to function independently, leading to combustion motors burning gasoline for nearly one-third of the distance covered in EV mode.

Regulatory and Financial Implications

According to estimates, the lowballing of PHEV emissions enabled several major carmaker companies to escape more than €5bn in fines from 2021 and 2023, by artificially easing compliance with EU average fleet CO₂ targets.

Furthermore, owners of PHEVs would pay approximately €500 extra annually in operating costs than is assumed under laboratory conditions.

“The bold statements that manufacturers like to make about their plug-in hybrid vehicles are clearly far from the mark,” stated a transport analyst. “Consumers are being misled into believing that by buying a PHEV, they are benefiting the environment and saving money. In reality, PHEVs are only slightly better than standard petrol and diesel vehicles in terms of energy consumption, CO₂ emissions, and running expenses.”

Political Debate and Automotive Lobbying

Hybrid cars have recently been brought again into policy discussions as carmakers have pressed the European Union to weaken CO₂ standards. A planned prohibition on sales of new combustion engine cars in 2035 has faced intense pressure from the automotive sector and opposition from member states with large automotive manufacturing.

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

One independent energy economics expert, who was not involved with the research, described the report a “very useful contribution” after years in which parts of the car industry argued there was insufficient information to accurately assess real-world emissions.

“These findings show, beyond any doubt, that the gap between lab and actual PHEV energy use and CO₂ output is significantly greater than for petrol or conventional vehicles,” they stated. “Any policy adjustments concerning PHEVs should be implemented with extreme care and considering this evidence.”