Plug-in hybrid electric vehicles are emitting far more carbon dioxide in everyday use than official figures suggest, according to an independent analysis that has prompted fresh calls for tighter rules and methodology changes across Europe.
According to a report by Transport and Environment, which examined hundreds of thousands of vehicle records, the real-world CO2 performance of PHEVs is dramatically worse than the reductions long cited by regulators and manufacturers. The NGO’s analysis found PHEVs deliver, on average, only around a 19% reduction in CO2 per kilometre compared with petrol and diesel cars, not the roughly 75% cut that has been used in policy calculations. The study drew on large datasets of post-2021 registrations to reach its conclusions.
The gap between laboratory-based estimates and what cars emit on the road has widened markedly in recent years. Transport and Environment’s data show that by 2023 real-world CO2 from PHEVs was almost five times higher than standard test results would imply, a divergence that researchers say cannot be explained away by normal variability in driving conditions.
A central reason for the disparity is how often PHEVs actually run on electric power. Regulators use a utility factor to estimate the share of kilometres driven electrically; the European methodology has assumed a very high electric share. But the empirical data reveal a much lower electric usage rate, with drivers using the combustion engine for the majority of their trips. Industry observers point to practical barriers such as limited fast-charging capability on many PHEV models and the convenience of refuelling with petrol as factors that reduce real-world electric kilometres.
The report also highlights that PHEVs are not zero-emission even when operating in their so-called electric mode. Transport and Environment calculated an average emission of about 68 grams of CO2 per kilometre during electric-mode operation, far above the single-digit grams per kilometre assumed in official calculations. That higher-than-expected emission in electric mode adds fuel costs for drivers and undermines consumer expectations that a PHEV purchase automatically delivers substantial climate benefits.
Researchers warn that the systematic underestimation of PHEV emissions has real regulatory and financial consequences. According to the analysis, major manufacturers benefited from the discrepancy when compliance and penalty calculations were made using the optimistic official figures, allowing some firms to avoid substantial fines for exceeding fleet CO2 limits. Transport and Environment and allied commentators contend this has distorted the market signal that should favour genuinely low- or zero-emission vehicles.
Brussels has signalled it will adjust the utility factor methodology and is preparing a broader review of car CO2 standards in 2026. Campaigners welcome those steps as necessary but say partial fixes will not close the gap unless the entire approach to assessing real-world PHEV performance is overhauled. The move faces resistance from parts of the automotive sector and trade associations lobbying to preserve the status quo, arguing for continued recognition of PHEV contributions under current rules.
Across the Atlantic, market dynamics differ but raise parallel concerns. Rising retail prices for battery-electric cars and the changing landscape for purchase incentives have left some US consumers more receptive to hybrid alternatives. Preliminary sales data show growing interest in standard hybrids while demand for PHEVs has been largely flat, suggesting that neither market nor policy developments have yet delivered a clear shift to fully electric mobility in all regions.
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