There is no first and second class anymore. There's something called NSB Komfort that only costs NOK 75 (USD 12) each way no matter how long the journey is.

It's worth the money! You get a table, more legroom, PC power, free Coffee and Tea and free newspapers. It doesn't have to be booked in advance, but to get the best seats, it might be worth getting the ticket online

http://www.nsb.no/internet/no/Guide_...b=&language=no

Sorry, Norwegian only