Business 18 February 2026, 1:35pm

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The research was conducted by the Fraunhofer Institute for Systems and Innovation Research (Fraunhofer ISI) and several partner institutions. The results were reported by the German public broadcaster Südwestrundfunk (SWR). The analysis was based on real-world usage data from almost one million vehicles manufactured by several car manufacturers between 2021 and 2023.

According to official measurements, the average fuel consumption of plug-in hybrids is around 1.5 litres per 100 kilometres.

However, real-world road data shows an average of around six litres per 100 kilometres.

This results in higher fuel costs and carbon dioxide emissions.

According to the study, one reason for the discrepancy is that cars consume an average of three litres of fuel per 100 kilometres, even when operating predominantly in electric mode — much more than was previously assumed. Patrick Plötz, the head of the research at Fraunhofer ISI, told SWR that this result came as a real shock to the researchers.

However, the difference may be smaller for newer plug-in hybrids, as fuel consumption measurement rules have tightened in the meantime.

However, researchers are urging the European Union to align its regulations further with actual road data. They believe that the discrepancy between 'theoretical' and 'actual' consumption is too significant, and that stricter calculation requirements are therefore needed for plug-in hybrids.

This would also impact car manufacturers, as compliance with EU fleet-level carbon dioxide emission targets is currently monitored using values obtained via the Worldwide Harmonised Light Vehicle Test Procedure (WLTP).

According to Patrick Plötz, the technical conditions and data are now in place to evaluate cars based not only on type approval documents, but also on their actual performance on the road.

Cover image (for illustration purposes only): Getty Images