Plug-in hybrid electric cars (PHEVs) use much more fuel on the road than officially stated by their manufacturers, a large-scale analysis of about a million vehicles of this type has shown.
The Fraunhofer Institute carried out what is thought to be the most comprehensive study of its kind to date, using the data transmitted wirelessly by PHEVs from a variety of manufacturers while they were on the road.
The cars involved were all produced between 2021 and 2023. The data transmitted enabled analysts to determine their precise and real-world fuel consumption, as opposed to that stated in the vehicles’ official EU approved certification.
PHEVs, cars which combine a petrol or diesel engine with a battery-powered electric motor that is charged from an external energy point, give drivers the flexibility to be able to switch between the ecologically safer power source, and the more conventional, but environmentally more damaging one, as and when conditions allow. Manufacturers typically market the vehicles as energy efficient. On paper at least, the vehicles are said to use much less fuel, between one and two litres per 100km, than conventional cars. However environmental groups have long since voiced scepticism over the claims.
According to the study, the vehicles require on average six litres per 100km, or about 300%, more fuel to run than previously cited.
I'm not sure about this study (can't read any German oops), but expected vs real-life usage of PHEVs (Plug-in Hybrid) is exactly the problem brought up by T&E and others at the end of last year, see for example this report from October 2025:
I'm not doubting at all that you outperform the expected consumption, but sadly on average it seems like there's more of a systematic (and significant) under-performance. However, this is comparing WLTP testing to real-life driving EU data, for cars sold in the EU. I'm sure that this might be region-dependent as models and driving habits might be radically different.
EDIT: oops as mentioned by @Don_alForno@feddit.org, this seems to be more about the engine of certain manufacturers consuming more than expected in electric drive mode:
So not the same as the T&E study, and much less about usage.
My experience is only with the Chevy Volt which was sadly discontinued. The Volt's engine will occasionally come on if I'm accelerating from speed, like in a short merge to a fast expressway, but that doesn't last long. Aside from that and burning old gas, the engine never comes on while the battery has charge. I have no idea how other plugins function.