Norway in a Nutshell trains are booked!

I can't say whether or not this is the norm, but we flew into Bergen last year for the Bergen-Oslo route (overnight in Balestrand) and it was fantastic. Norwegian should have cheap flights from Oslo and often.

You may want to consider calling the reservations number and ask if there might be additional cars added to the train due to demand or if your idea of traveling in the opposite direction is the only option. There is really no difference which way you go...the scenery is the same. If you are going from Oslo to Myrdal you should sit on the left side of the train. Traveling east you should sit on the right.

Are you trying to travel towards Myrdal at the start of Easter (Påske) Week where every other Norwegian is heading for their mountain hytte? The trains heading towards the Hardangervidda will be packed with Norwegian families carrying skis and provisions for a week in the mountains starting the weekend before Easter Sunday. Then the flow will reverse the Monday after Easter.

PS Oslo will be empty and stores and restaurants on limited hours from Påske Thursday through the Monday after Easter. Norway will be on a four day holiday and it seems as if half of Norway is in the mountains.

http://publicholidays.eu/norway/
2016:
24 Mar Thu Maundy Thursday
25 Mar Fri Good Friday
27 Mar Sun Easter Sunday
28 Mar Mon Easter Monday

https://en.wikipedia.org/wiki/List_of_minimum_annual_leave_by_country
Norway:

Employers are required that employees have 25 working days of leave in
connection with holidays each holiday year. All days count as working
days except Sundays and statutory church or public holidays. Workers
are also entitled to two paid public holidays.

Norwegians like to take at least a week off during winter of their 5 weeks of leave. And that week is usually Easter week.

Thanks for all of your replies so far. I thought about flying up to Bergen immediately after arriving at the Oslo airport and doing the tour in reverse, but will the last bit on the way back to Oslo be in the dark?

I will try calling to see if there are extra train cars. That would be ideal.

I didn't realize that the week before Easter would be so busy. If we end up having to stay in Oslo for the 4 nights (18 March to 21 March), I hope we aren't too horribly bored.

Any suggestions?

Have you tried the Fjord Tours agency: https://www.norwaynutshell.com/
A Monday or Tuesday start may be between the start of Easter week weekend rush to the mountains or Good Friday when everyone is where they want to be. Oslo will be pretty "dead" with a lot of businesses shut or on reduced hours.

ADDED: http://secure.fjordtours.com/tour/date.aspx
Fjord Tours is showing March 21,22 and 25,26 one way from Oslo as available.

"will the last bit on the way back to Oslo be in the dark? "

Even if it is, that is, by far, the least impressive part of the route. So don't worry, if that's the only way you can make this work.