Thanks for the information.

It seems that nsb.no has got its web site and booking engine slightly out of sync - dates become clickable on the web site two days before you can make bookings. Someone must have miscounted!

It's not really Oslo we need to get to... our final destination is home (NWI in England). Our conference in Trondheim ends on Thursday, and we had hoped to fly home from TRD on Friday (via AMS), but found that fares were pretty extortionate - probably because it's the beginning of the holiday week-end. The choice, thus, was between hanging around in Trondheim for another day or going somewhere else... and as we're on an open-jaw itinerary anyway we thought we'd look into flying home from OSL on the Saturday and taking a leisurely train ride on Friday.

We've now decided to do something slightly different... we're going to Lillehammer instead of Oslo (a trip down Memory Lane for me, I spent a very enjoyable week there in the 1990s). Train, hotel and flight from OSL to NWI are now all booked.