Have any comments re driving in Norway/Sweden/Denmark and cost of fuel?
I can't comment on the price of fuel beyond "expensive", but should that surprise you in Norway?
But, here is one pratical tip for driving in Norway. The toll roads, if you drive on one, are rather non-intuitive. Rather than me trying to explain, here's the link. If you're renting the car in Norway, the agency should be able to explain the system, and the car likely already comes equipped with the pass. If you plan to pick up the car in Sweden or Denmark, it might be a little more complicated.
Try this website to compare gas prices
Norway is most expensive in world at average of $10.71 per gallon.
It is pretty easy to drive in Scandinavia.
In Norway, make sure you plan around the ferry times if you are driving in the fjord region.
Stockholm has a congestion tax you pay when entering city. I don't know how this works with a rental car.