Large-scale German research reveals Plug-In Hybrids use up to 300 % more fuel than advertised

What does the study reveal

The PHEVs analysed consumed an average of 5.9 litres of petrol per 100 km. On paper, many plug‑in hybrids score around 1 to 2 litres per 100 km under WLTP testing. In real‑world use, however, the picture is very different.

Even more striking is that, even in the so‑called primarily electric driving mode, PHEVs still consume an average of 3 litres of petrol per 100 km.

Researcher Patrick Plötz describes this as “a shock”. The expectation was that fuel consumption in this mode would be close to zero. The data shows otherwise: the combustion engine engages far more frequently than anticipated.

Why is the gap so large

Plug‑in hybrids rely on two propulsion systems:

• an electric motor with a battery

• a conventional internal combustion engine

Official WLTP tests assume a high share of electric driving. In reality, drivers charge less often than expected, or the system itself switches to the combustion engine more quickly.

The result is theoretically low figures on paper, but much higher real‑world consumption. The study therefore suggests that the current European test regime does not adequately reflect real‑life usage.

Is it all bad news

Not entirely. When comparing average PHEV consumption with that of a conventional petrol car, the picture becomes more nuanced. An efficient city car such as a Hyundai i10 averages around 5.8 litres/100 km in real‑world driving. That is almost identical to the average consumption of the plug‑in hybrids analysed.

In other words, a PHEV is not exceptionally efficient in practice, but neither is it dramatically worse than an efficient petrol car. The real issue lies in the contrast between marketing claims and reality.

German brands show higher consumption, Porsche at the bottom of the table

According to the analysis, German PHEV models rank among the higher consumers on average. Plug‑in hybrids from Porsche, such as the Cayenne E‑Hybrid and Panamera E‑Hybrid, show particularly high consumption in discharge mode.

That is not entirely surprising. Performance‑oriented plug‑in hybrids naturally encourage spirited driving. And yes, driving style has a significant impact on consumption.

Porsche itself rightly points to usage patterns as the key explanation. WLTP measurements follow legal procedures, but individual real‑world use varies widely. Brands such as Kia, Toyota, Ford and Renault achieve the lowest real‑world consumption figures in the study.

What does this mean for Europe

The study puts pressure on the EU to reassess its regulations around type approval and fleet averages. Today, official WLTP values are used to calculate manufacturers’ CO₂ fleet targets.

If real‑world consumption is structurally higher, climate targets may be met on paper, but not necessarily on the road. The researchers therefore argue for integrating real‑world usage data into future regulations.

So has the plug‑in hybrid failed?

Not necessarily. A plug‑in hybrid works perfectly when used correctly:

• regular charging

• short trips driven electrically

• long journeys using a combined approach

Without discipline, however, it quickly turns into a heavy petrol car carrying additional technology. The technology itself is not the problem. Usage patterns often are.

The coming years will determine whether PHEVs remain a transitional technology or gradually disappear between full EVs and efficient mild hybrids. One thing is certain: figures on paper are no longer enough.