Word of caution here. We were in Oslo in March 2010 and the local train (NSB) was delayed at the airport for over half an hour - pretty cold standing on Gardermoen platform. Then on our way back to the airport on the Sunday morning the local NSB train was completely cancelled and only for the assistance of a local we could have missed our flight. So the tip is take the NSB on arrival in Gardermoen Airport if you like - but take the FLYTOGET Express Train on you your way back to the airport at the end of your break !!