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Plug-in hybrid cars produce nearly 5x more planet-heating pollution than lab-reported data indicate, according to a new analysis.

Widening Gap Between Official and Real-World Emissions

Statistics reveals that PHEVs release only one-fifth lower CO₂ than traditional petrol and diesel vehicles, based on analysis carried out by a advocacy organization. That differs sharply with laboratory tests, which assumed a 75% reduction in emissions.

Researchers studied data from onboard fuel consumption monitors of 800,000 cars sold in Europe from 2021 and 2023. The team discovered that actual CO₂ output from PHEVs in 2023 were nearly five times higher than official estimates, up from three and a half times in 2021.

“Real-world CO2 output are increasing, while official emissions are falling,” said a senior researcher participating in the report. “That gap is widening and creates a significant issue. As a result, PHEVs pollute almost as heavily as petrol cars.”

Key Reasons Behind 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 total distance. The team found that just a quarter of driving was done in electric mode, whereas lab estimates assumed 84%.

Even, when running in EV mode, emission amounts were well above lab projections. That occurred because EV motors were insufficiently powerful sufficient to operate alone, resulting to engines using gasoline for almost a third of the distance completed in electric mode.

Policy and Financial Implications

Based on estimates, the underestimation of PHEV emissions allowed several major automaker groups to escape more than €5bn in fines from 2021 and 2023, by artificially easing compliance with European Union fleet-average CO₂ standards.

Additionally, drivers of PHEVs would spend approximately €500 extra annually in running costs than would be estimated under laboratory tests.

“The strong claims that manufacturers like to make about their PHEV vehicles are obviously way off the truth,” commented a transport analyst. “Consumers are being misled into thinking that by buying a PHEV, they are benefiting the environment and saving money. In reality, PHEVs are only slightly improved than standard petrol and diesel vehicles in terms of fuel use, CO₂ production, and operating costs.”

Policy Discussion and Industry Pressure

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

Several senior officials have proposed PHEVs as a possible “compromise” option to introduce in the legislation.

One external energy economics specialist, who was not involved with the study, described the analysis a “highly valuable contribution” after years in which parts of the automotive sector argued there was too little data to properly assess real-world emissions.

“These findings show, without question, that the gap in lab and actual PHEV fuel consumption and CO₂ emissions is significantly larger than for petrol or diesel vehicles,” they said. “All policy adjustments concerning PHEVs should be made with extreme caution and considering that data.”