This list can not be right. It seems, because of the population numbers and the inclusion of Porsgrunn/Skien, this is in fact a list of largest "urban areas", not "cities". If so, Tromsø should not be included (not even in 2013). As of 2016, that list would read: Oslo, Bergen, Stavanger/Sandnes, Trondheim, Drammen, Fredrikstad/Sarpsborg, Porsgrunn/Skien, Kristiansand, Ålesund and Tønsberg.
The biggest Norwegian cities, as of 2016 (and probably also of 2013) are: Oslo, Bergen, Trondheim, Stavanger, Bærum (part of the Oslo area), Kristiansand, Fredrikstad, Sandnes, Tromsø and Drammen.
Fredrikstad and Sarpsborg are two different cities, and if they are to be placed together (as in one of the most populous urban areas of Norway), they are always written together as Fredrikstad/Sarpsborg or Sarpsborg/Fredrikstad.
The biggest Norwegian cities, as of 2016 (and probably also of 2013) are: Oslo, Bergen, Trondheim, Stavanger, Bærum (part of the Oslo area), Kristiansand, Fredrikstad, Sandnes, Tromsø and Drammen.