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Plug-in hybrid cars produce almost 5x greater global warming pollution than lab-reported data indicate, according to a new analysis.

Widening Discrepancy In Official and Actual Emissions

Statistics shows that PHEVs release just 19% less CO₂ than conventional petrol and diesel vehicles, based on research conducted by a non-profit group. That contrasts sharply with laboratory estimates, which assumed a three-quarters reduction in emissions.

Analysts studied data from in-vehicle fuel consumption meters of eight hundred thousand cars sold in the EU from 2021 and 2023. The team found that real-world CO₂ emissions from PHEVs in 2023 were nearly five times greater than lab figures, increased from 3.5 times in 2021.

“Actual emissions are rising, while lab-reported figures are falling,” stated a senior researcher involved in the study. “This gap is growing and poses a significant issue. Consequently, PHEVs emit nearly as heavily as gasoline vehicles.”

Primary Factors Driving the Emissions Gap

Researchers linked most of the difference to inflated estimates of the “utility factor” – the ratio of kilometers travelled in electric power compared to overall distance. They found that just a quarter of driving was completed in EV mode, while lab assumptions assumed over four-fifths.

Additionally, when operating in EV mode, pollution levels were well above lab estimates. That happened because electric motors were not strong enough to operate alone, leading to engines using fossil fuels for nearly a third of the distance covered in EV mode.

Regulatory and Economic Consequences

According to calculations, the underestimation of PHEV CO2 output enabled four major automaker groups to escape more than €5bn in penalties from 2021 and 2023, by artificially easing compliance with European Union fleet-average CO₂ targets.

Additionally, owners of PHEVs would spend approximately €500 more annually in operating costs than is assumed under lab tests.

“The strong statements that automakers like to make about their PHEV cars are clearly way off the truth,” commented a automotive expert. “Buyers are being misled into believing that by buying a PHEV, they are benefiting the environment and cutting money. In reality, PHEVs are only slightly better than standard petrol and diesel vehicles in terms of fuel use, CO₂ production, and running costs.”

Policy Debate and Automotive Pressure

Plug-in hybrid vehicles have recently been brought back into policy debates as carmakers have lobbied the European Union to relax CO₂ targets. A proposed prohibition on sales of new internal combustion vehicles in 2035 has faced heavy lobbying from the car sector and resistance from member states with significant car industries.

Some high-level officials have suggested PHEVs as a possible “flexibility” option to introduce in the legislation.

An external energy economics expert, who was unaffiliated with the research, called the analysis a “very useful contribution” after a long period in which parts of the car sector claimed there was too little data to properly assess real-world CO2 output.

“The results demonstrate, beyond any doubt, that the difference between official and real-world PHEV fuel consumption and CO₂ output is much, much greater than for petrol or diesel cars,” they said. “All policy changes concerning PHEVs should be made with utmost caution and in the light of that evidence.”