Cars are taxed based on price, engine size and environmental factors. The end result is that mid to high end gas cars with a big engine can easily cost 3 times as much in Norway as elsewhere, and some models are modified to be delivered with smaller engines in Norway to reduce the tax.
And then what happens is that people buy cars from neighboring countries and register them there. Happens here in Romania. A lot of people (overall a small percentage of all the cars on the road, true), register their cars in Bulgaria. Especially from Bucharest easy it's - just a 60km drive to the nearest Bulgarian town where the car can be registered/serviced.
Very rarely in Norway. If you're stopped at a routine traffic stop with a Norwegian drivers license, driving a foreign-registered car, the police will expect you to be able to show customs documents from the border to document that the car has been registered on entry. If you can't do that, or if the car was imported more than 30 days ago, you're in for a world of hurt. For most people it's not worth the risk
