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Plug-in hybrid cars produce nearly 5x greater planet-heating pollution than official data show, according to a new analysis.

Growing Discrepancy Between Official and Real-World Emissions

Statistics reveals that PHEVs release just 19% lower CO₂ than conventional petrol and diesel cars, based on research carried out by a non-profit group. That contrasts sharply with laboratory estimates, which suggested a three-quarters decrease in emissions.

Analysts examined information from in-vehicle fuel consumption monitors of 800,000 cars registered in Europe from 2021 and 2023. The team discovered that actual CO₂ output from PHEVs in 2023 were nearly five times greater than lab figures, up from 3.5 times in 2021.

“Real-world emissions are rising, while official figures are decreasing,” stated a lead researcher participating in the study. “This gap is widening and creates a serious problem. As a result, PHEVs pollute almost as heavily as petrol vehicles.”

Primary Reasons Driving the Discrepancy

Analysts attributed most of the gap to inflated estimates of the “utility factor” – the percentage of miles driven in electric power relative to overall mileage. The team found that only 27% of driving was done in electric mode, whereas lab estimates suggested 84%.

Even, when operating in EV mode, emission amounts were significantly higher than official projections. That happened because EV motors were insufficiently powerful enough to function independently, resulting to engines burning fossil fuels for almost one-third of the distance covered in electric mode.

Regulatory and Economic Implications

According to estimates, the underestimation of PHEV emissions enabled four large automaker companies to avoid over €5bn in fines between 2021 and 2023, by artificially simplifying adherence with European Union average fleet CO₂ standards.

Furthermore, owners of PHEVs could spend approximately €500 more annually in running expenses than is estimated under laboratory conditions.

“The strong claims that manufacturers like to make about their plug-in hybrid cars are clearly far from the mark,” commented a transport analyst. “Buyers are being duped into believing that by buying a PHEV, they are benefiting the environment and saving costs. In reality, PHEVs are little improved than regular gas and diesel vehicles in terms of fuel consumption, CO₂ production, and running costs.”

Political Discussion and Automotive Lobbying

Plug-in hybrid cars have lately been drawn back into political debates as automakers have pressed the EU to relax CO₂ standards. A proposed prohibition on sales of new internal combustion cars in 2035 has faced heavy lobbying from the automotive sector and resistance from member states with large car industries.

Several high-level politicians have proposed PHEVs as a potential “compromise” option to include in the legislation.

An external energy economics expert, who was unaffiliated with the study, described the analysis a “very useful contribution” after a long period in which segments of the car industry argued there was insufficient data to properly assess real-world CO2 output.

“These findings demonstrate, without question, that the gap between lab and actual PHEV fuel consumption and CO₂ output is significantly greater than for petrol or diesel vehicles,” they stated. “All policy changes concerning PHEVs should be implemented with extreme care and considering that data.”