A new study by Transport and Environment (T&E), “Europe’s leading advocates for clean transport and energy,” says plug-in hybrid electric vehicles (PHEV) are nearly as dirty as gas cars. This marks another reason plug-in hybrids may not be a great step towards EV adoption after all.
“In the real world, plug-in hybrids emit 135g of CO2 per km on average, according to T&E analysis of data gathered by the European Environment Agency (EEA) from fuel monitors on 127,000 vehicles registered in 2023. Petrol and diesel cars emit 166g of CO2/km on average.”
T&E researchers analyzed emissions data from 127,000 PHEVs registered in the European Union in 2023. The study, using data gathered by the European Environment Agency (EEA), found that those PHEVs produced carbon dioxide (CO2) emissions nearly five times higher in the real world than tests conducted under lab-conditions suggest. That means that instead of PHEV delivering a 75% reduction in emissions as originally indicated by lab tests, they only produce 19% less pollutants.
One reason plug-in hybrid vehicles for sale in the U.S. produce excessive emissions is they’re typically heavier than more economical vehicles, not to mention it’s unknown how often owners actually charge their vehicles. The T&E study found that PHEVs with electric-only ranges exceeding 75 km produced more CO2 emissions than shorter-range PHEVs due to the increased weight of the larger batteries.
“PHEV emissions are also increasing because of the trend towards longer electric ranges as bigger batteries make the vehicles heavier and, therefore, burn more fuel in engine mode. These heavier vehicles also consume more energy than smaller cars when driven on the battery.”
The underlying reason for the excessive PHEV emissions is that the electric drive motors they use don’t actually have enough power to propel the vehicle under all conditions, such as “higher speeds or steep inclines.” Instead, the PHEV uses its gas engine to compensate, burning up to three liters of fuel per 100 kilometers (0.8 gallon per 62 miles) even while operating in electric mode. That results in an electric-only-mode emission of 68g of CO2 per kilometer, or about 8.5 times the official prediction.

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