Great trip. The Oslo pass was well worth it. On the 48 hour pass we had unlimited access to public transportation, even tho our passes were never checked. We were able to figure out the tram and bus routes and, when we were uncertain, Oslo people were very friendly and helpful. We visited 3 museums, the Nobel Peace Center and the Reptile Park...all free with our pass. That was enough sight-seeing for us.
The Olso Pass is definitely worth obtaining. You have access to most of the museums and public transportation. We purchased the 72 hour option but there is also a 48 and 24 hour option. It will save you money and also save time.
I was on a layover so I had a limited amount of time and mistakenly thought that if I bought a pass online I would be able to zip through the process. I was wrong. Instead I waited almost two hours to get my pass at their tourist office so I was barely able to use it. The other issue was that the only place, and the only tourism office is at the train station, which meant that it was a 30 minute ride from the airport to the station. Was also impossible to get cash from the ATMs at the airport, which turned out to be a good thing. Expensive and wasted my time on line. If you need to use the bathroom at the train station, be prepared to pay.