Plug-in hybrids emit six times more CO2 than officially stated

The gap between official and real CO₂ emissions from plug-in hybrids continues to grow. According to a new analysis by Transport & Environment, PHEVs emitted on average about six times more CO₂ under real-world conditions in 2024 than official figures suggest.

According to T&E, real PHEV emissions are far above official figures.

Image: Florian Treiß

Transport & Environment (T&E) bases its analysis on data from the European Environment Agency. According to this, the real-world CO2 emissions of plug-in hybrids registered in 2024 were, on average, about six times higher than the official figures. In 2023, T&E reported that this factor was still around five.

For drivers, this discrepancy also has financial consequences. T&E calculates that the additional fuel costs – compared to official consumption figures – for a PHEV sold in 2024 amount to an average of €680 per year. Even compared to conventional internal combustion engine vehicles and non-plug-in hybrids, the real-world advantage is smaller than the official figures suggest. According to T&E’s analysis, the actual emissions of plug-in hybrids were only 14 per cent lower than those of these vehicles. In contrast, official test values suggested a reduction of 83 per cent.

According to T&E, one reason for this is that the internal combustion engine also runs regularly during supposedly electric operation. The analysis found that this was the case for about one-third of the kilometres driven in battery mode.

A gap between the test bench and real-world conditions is not a new problem, as demonstrated by the International Council on Clean Transportation (ICCT) this summer. In an evaluation of around eight million vehicles, the researchers found that in 2023, real-world PHEV emissions were, on average, about five times higher than official test values. The ICCT cited causes such as lower electric driving performance than assumed, frequent use of the internal combustion engine, and the additional weight of the dual powertrain.

Disputing the ‘utility factor’ in CO2 reduction

At the heart of current regulations lies the so-called utility factor. This determines what proportion of a plug-in hybrid’s mileage is assumed to be electric when calculating official CO2 emissions. The EU has already adjusted this factor to bring type-approval values closer to real-world usage.

The automotive industry is now also exploring how to technically enforce a higher proportion of electric driving. In 2025, the VDA proposed designing future plug-in hybrids so that they must be charged regularly. If charging does not occur within a yet-to-be-defined driving distance, the powertrain output could be throttled. The proposal was intended to address the criticism that the real-world electric driving share of PHEVs has so far been difficult to ensure.

T&E already sees a technical effect in the first correction. The organisation analysed 20 of the best-selling PHEV models, which together accounted for 51 per cent of sales in 2025. According to the analysis, manufacturers responded, among other things, with larger batteries and increased electric ranges.

According to T&E, the adjustment was particularly pronounced in models from the Volkswagen Group. For the VW Tiguan, the electric range increased from 55 to 119 km. As a result, official emissions were kept at 36 g CO2/km despite stricter calculations, compared to 32 g/km previously. For five VW models examined, around 90 per cent of the increase in official emissions caused by the utility factor correction was compensated in this way.

In T&E’s assessment, manufacturers could also absorb the next adjustment through further technical improvements. For example, by increasing electric range, improving the efficiency of internal combustion engines, reducing weight, enhancing aerodynamics, and optimising recuperation. The organisation believes it is possible to keep PHEVs below the 50 g CO2/km threshold.

However, the next correction is politically contentious. T&E warns against freezing the utility factor at the 2025/26 level. According to the organisation’s calculations, real-world PHEV emissions would still be underestimated by 56 per cent.

This would not only affect the consumption figures provided to customers. Low estimated PHEV emissions also impact the CO2 fleet balance of manufacturers and can thus influence how many pure electric cars need to be sold to meet European fleet targets.

The ICCT had already pointed out that the latest correction is insufficient to fully reflect real-world PHEV emissions. Both analyses thus arrive at a similar conclusion despite different data bases. After all, the climate balance of plug-in hybrids depends not only on their technical design but, above all, on how often they are actually driven and charged electrically.