Marte Skogstad Allgot moved back to Oslo, Norway, from London two years ago and soon found that running a car on gas was prohibitively expensive.

To her surprise, Allgot discovered it was cheaper to run a fully-electric Tesla Model S car than it was to drive a hybrid Toyota Prius.

"When we added up how much we were spending on tolls and fuel it was the equivalent of buying a Model S," she told CNBC. "I still can't believe that buying what I consider to be an expensive, luxury car makes more economic sense than owning a Prius."

Only full-electric vehicles in Norway don't pay tolls erected on city boundaries, and Allgot said the costs soon add up.

"The toll system is electronic so you don't notice the 54 Norwegian crowns ($7) every time, but when you see that bill at the end of the month you have to ask whether it is worth it," she said.

Allgot's solution was to buy a Tesla Model S, which retails for the equivalent of $80,000 in Norway. Incredibly, the country's fourth most popular car is the more expensive Model X, with a list price of $125,000.

Tesla isn't the only popular electric or hybrid vehicle in the northern European country. Across 2017, and for the first time ever, electric and hybrid cars accounted for more than half of all new vehicle sales in Norway.