Plug-in hybrid cars have long been promoted as a practical compromise between conventional vehicles and fully electric models. However, new European research suggests their environmental performance may be considerably less impressive than official figures indicate.

An analysis by environmental organisation Transport & Environment (T&E) found that plug-in hybrids registered in the European Union in 2024 produced approximately six times more carbon dioxide during real-world driving than their official ratings suggested.

The findings have intensified debate over vehicle emissions testing, manufacturer responsibilities and the future of Europe's automotive regulations.

What Did The Research Reveal?

Researchers examined data collected by onboard monitoring systems in approximately 220,000 plug-in hybrid vehicles. The results showed that cars registered in 2024 emitted an average of 145 grams of CO₂ per kilometre, compared with their official rating of just 24 grams.

The difference was even greater than in the previous year. Plug-in hybrids registered in 2023 produced an average of 138 grams per kilometre, against an official figure of 28 grams. This means real-world emissions increased by approximately 5%, while official ratings declined by around 15%.

Although plug-in hybrids still performed better than conventional petrol and diesel vehicles, their advantage was relatively modest. Traditional combustion-engine cars emitted an average of 169 grams of CO₂ per kilometre, making plug-in hybrids approximately 14% cleaner based on tailpipe emissions.

Why Are Official Figures So Different?

Plug-in hybrids combine an internal combustion engine with a rechargeable battery and electric motor. When regularly charged, they can complete shorter journeys using electricity, reducing fuel consumption and tailpipe emissions. However, their actual environmental performance depends heavily on how frequently drivers recharge their batteries.

Official emissions calculations use a measurement called the utility factor, which estimates the proportion of driving completed using electricity. If the calculation assumes more electric driving than owners actually achieve, the resulting emissions rating can be significantly lower than real-world figures.

Consequently, vehicles that are rarely charged may consume considerably more fuel than buyers expect.

Why Are Carmakers Opposing New Rules?

The European Union began adjusting its emissions calculations in 2025 to better reflect real-world driving conditions. A further correction is scheduled for 2027, but automotive industry representatives are pushing for its cancellation. The European Automobile Manufacturers' Association (ACEA) has opposed the proposed adjustment. Horse, a powertrain joint venture involving Renault and Geely, has also argued that stricter calculations could create additional challenges for manufacturers.

The disagreement matters because official emissions ratings determine whether carmakers meet the EU's fleet-wide CO₂ targets. A vehicle producing 145 grams per kilometre in everyday driving may currently count as emitting only 24 grams for regulatory purposes.

Could Europe's Climate Goals Be Affected?

The debate comes as European policymakers consider changes to the rules governing new vehicles after 2035. An earlier proposal would reduce the required emissions reduction from 100% to 90%, potentially allowing some combustion-engine vehicles to remain available.

Industry proposals have called for a further reduction to 80%, alongside more flexible compliance arrangements. T&E estimates that adopting the broader package of proposed changes could increase Europe's oil import costs by €74 billion between 2026 and 2035.

The organisation also projects up to 2.4 billion additional tonnes of CO₂ emissions by 2050 under that scenario. These figures are projections based on proposed policy changes, rather than outcomes already observed.

What Does This Mean For Drivers?

Plug-in hybrids accounted for approximately 9.8% of new EU vehicle registrations during the first half of 2026. For motorists who regularly recharge and primarily make short journeys, the technology can still provide meaningful fuel savings.

However, drivers who frequently travel long distances or rarely charge their vehicles may experience substantially higher fuel consumption. The findings underline the importance of considering everyday driving habits alongside official efficiency ratings.

What Happens Next?

European policymakers face growing pressure to balance automotive competitiveness with environmental commitments.

Stricter testing methods could make vehicle ratings more representative of actual emissions, while manufacturers argue that regulatory flexibility is necessary during the transition towards electric mobility. The central question is whether future regulations will reflect how plug-in hybrids are used on the road.

For consumers and policymakers alike, accurate emissions figures will be essential for making informed decisions about Europe's automotive future.