Major study reveals plug-in hybrids use four times more fuel than claimed

20 February 2026

The automakers around the world paint plug-in hybrids (PHEVs) as the perfect bridge to a cleaner future. These vehicles carry both a battery and a gasoline engine, promising the best of both worlds. But a huge new study reveals that this "bridge" might be built on a very shaky ground. Research from the Fraunhofer Institute shows that these cars are gulping down far more gasoline than the official labels suggest.

The study looked at data from nearly one million vehicles across Europe. It found that, on average, these cars use over 300% more fuel than government tests claim. Carmakers say these EVs are helping the planet, but the numbers from the road tell a very different story. Instead of the tiny sips of fuel promised in brochures, these cars appear to have a drinking problem.

Government-sanctioned efficiency tests in Europe (WLTP) once suggested that a typical plug-in hybrid would use only about 1.57 liters of fuel for every 100 km - that's roughly 150 miles per gallon. But when researchers looked at the real-world data from 981,035 vehicles, they found the actual average was 6.12 liters per 100 km. That's about 38 miles per gallon - not an impressive number at all, more inline with a decent diesel car.

This means that electric cars with a backup engine are using nearly 3.9 times more fuel than advertised. The study used special monitors inside the cars to track exactly how much gas they burned. The huge data set covered almost every type of driver and model, making the results hard to ignore. It turns out that the "perfect" hybrid often ends up acting just like a regular gas car.

You might think that even if the gas engine is running, the battery should still be doing most of the work. The study looked at this too. They checked the "charge depleting" mode, which is when the car tries to use its battery power first. Even in this "cleaner" mode, the cars still used 0.1052 ft³ per 62 miles - almost double the average expected by the regulators.

Why does this happen? It seems the gasoline engine wakes up more often than anyone expected. It might kick in to help the car speed up, to run the heater on a cold morning, or simply because the battery is low. Even when drivers think they are driving purely on electricity, the tailpipe is often still puffing out smoke. The engine is rarely truly asleep.

The researchers also noticed a strange trend among different car brands. The expectation was that people who buy expensive cars would have the money to install a charger at home. Surprisingly, the data showed the opposite. Owners of budget-friendly brands tended to charge their cars more often, and those who bought luxury brands like Porsche, Bentley, or Ferrari rarely plugged them in at all.

The study specifically pointed at Porsche. The average Porsche in the group was only charged enough to provide 7 kWh of electricity over a distance of 16,780 miles. Even more shocking, more than half of the 11,307 Porsche vehicles in the study were never plugged in a single time. For these owners, the heavy battery is just extra weight they carry around while they burn gasoline, and it suggests those vehicles were simply bought for their lower tax burden.

It is common for gas cars to use about 20% more fuel on the road than they do in a lab. Most drivers accept this small difference. But for PHEVs, the 300% gap is a different beast entirely. It makes it very difficult for governments to set fair rules for pollution. If a car claims to be "green" but acts "gray," the environment pays the price. That means we all pay the price.

European regulators are now trying to fix these rules. They want to change the "utility factor." New rules will give these hybrids much less credit for being clean, bringing the official numbers closer to what is actually happening on the street.

As expected, not everyone is happy about these new rules. Companies that make combustion engines have spent a century perfecting them, and they want to keep selling those engines as long as possible. Some industry groups are lobbying to stop the government from changing the math. They argue that the current numbers are fine and that hybrids should play a long-term role in transportation.

But the Fraunhofer study warns that if the rules aren't tightened, it could result in 23 to 25 million extra tons of carbon dioxide entering the air over the next 20 years. That is a lot of extra pollution just because the labels on the cars were wrong.

Some experts have suggested other ways to make drivers use their batteries more. One idea is "display transparency," where the dashboard shows exactly what percentage of the trip was powered by gas versus electricity. Another, more extreme idea is "inducement," which would force the car to stop or slow down if the driver doesn't charge the battery every 311 miles.

The study concludes that these small nudges won't be enough. The best way to fix the problem is for the governments to be honest about how much fuel these cars actually use. By updating the rules for 2027, officials can finally close the gap between the glossy brochures and the reality, but for now, the "bridge" to the future looks a lot more like the past we are trying to move away from.

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