Real-world data reveals plug-in hybrids emit up to five times more CO₂ than official estimates, challenging Europe’s decarbonization goals.
How plug-in hybrid cars really work
The debate over the emissions of plug-in hybrid cars (PHEVs) is far from settled. According to a new analysis by Transport & Environment (T&E), Europe’s leading organization for transport decarbonization, the real CO₂ emissions from plug-in hybrids registered in 2023 are about five times higher than previously accepted figures.
The discrepancy stems from unrealistic assumptions about how often these cars are driven in fully electric mode. The report exposes a distorted system based on idealized rather than actual driving patterns.
Driving modes of plug-in hybrid cars
There are three key concepts that describe the main operating modes of a plug-in hybrid vehicle, which manage the use of the battery and the internal combustion engine at different times.
| Mode | Main Function | Role of Internal Combustion Engine (ICE) | Battery State of Charge Objective |
| Charge Depleting (CD) | Electric drive from the battery | Used only for extra power, such as steep climbs or acceleration | Deplete the battery |
| Charge Sustaining (CS) | Conventional hybrid drive | Provides main propulsion | Maintain steady charge with regenerative energy |
| Charge Increasing | Hybrid drive (ICE and/or Electric) | Powers the car and recharges the battery, increasing fuel use and emissions | Increase battery charge |
Real-world emissions underestimated
Official estimates drastically understate actual PHEV emissions because they assume an electric driving share (utility factor, UF) of 84%, while in reality, the figure is only around 27%.
As a result, combustion engines are used far more than expected, pushing real-world emissions well above laboratory figures.
Plug-in hybrids emit nearly as much as gasoline cars
T&E’s large-scale data analysis covering 127,000 vehicles registered in 2023 shows that average real-world CO₂ emissions from plug-in hybrids are 135 g/km, compared with 166 g/km for gasoline and diesel vehicles, a difference of just 19%.
This gap exists because official WLTP testing conditions fail to replicate typical driving behavior, leading to significant underreporting of emissions and fuel consumption.
What actually happens on the road
When driven in electric mode, PHEVs still consume an average of 3 liters of gasoline per 100 km, equal to 68 g of CO₂/km, 8.5 times higher than reported in official tests.
That’s because the electric motors in most plug-in hybrids lack the power to sustain high speeds or climb steep gradients, forcing the combustion engine to assist frequently. In practice, the gasoline engine contributes to nearly one-third of the distance supposedly driven in electric mode.
Hidden costs for drivers
PHEVs not only pollute more but also cost more. According to Bloomberg, their average retail price in Germany, France, and the UK is €55,700, about €15,200 more than a comparable battery electric vehicle (BEV).
In addition, drivers face hidden operating costs, about €500 extra per year in fuel and charging expenses, roughly 50% higher than expected. This happens because registration tests overestimate electric driving distances that rarely occur in daily use.
The European bluff
T&E’s report criticizes the European auto industry for lobbying the EU to allow plug-in hybrids to remain on sale after 2035, when new gasoline and diesel cars will be banned.
But if PHEVs’ real-world emissions are almost equivalent to traditional internal combustion engines, the move would be nothing short of a climate bluff, undermining efforts to cut transport-related CO₂.
To prevent this setback and secure Europe’s leadership in electric mobility, T&E calls for urgent action:
- Uphold the 2035 deadline: The EU must reject any attempt to weaken emission targets or introduce loopholes for plug-in hybrids.
- Tighten testing procedures: The “utility factor” (UF) measuring electric mode use should be updated every two years with real-world data, applying brand-specific coefficients to penalize higher emitters.
- Reward only true hybrids: Until 2035, incentives should go exclusively to PHEVs that deliver measurable environmental benefits, featuring stronger electric motors, at least 200 km of electric range by 2030, fast-charging capability (DC), and fuel tanks limited to 15 liters to compel regular charging.
Now, the ball is in Europe’s court. The next moves will determine whether the continent can maintain coherence and credibility in its decarbonization path, or give in to industrial lobbying and public mistrust.
