Can't help you with Oslo but...Schiphol Airport is about 13 miles from the Passenger Cruise Terminal in the centre of Amsterdam. You can take a No 370 bus from the Centre or a train to the station directly below the airport from the Central Station which takes about 15 minutes or a taxi from outside the terminal. Sorry I cannot at this stage give you the costs maybe some else can oblige with those. regards....Nei.
There are in general 4 train each hour from Schiphol airport to Amsterdam Central Station. If you take the northern exit from the station (construction going on for years, so changes are possible), you can walk the sidewalk for about 10-15 minutes. If you have much luggage this is not convenient and you must keep an eye on your belongings in the train, better keep it with you.
Or take a cab from the airport which will costs you around Eur. 40.- Till now cabs charged according the distance, but in the near future fix rates will be charged with addons for luggage etc. Cab ride will be around 20/30 minutes depending on traffic.
Well first you'll need to know where your ship is going to be docked. There are berths near the DFDS Ferry terminal, near the Color Line Terminal, near the Stena Line terminal and then again a berth or two in between these.
The easiest way then would be a taxi all the way from the airport OSL to your ship. However OSL is way out and this would be a very expensive option. More cost-effective would be to take the SAS bus from the airport to downtown and then a taxi to the ship.
To go from the airport to the cruise terminal - I would recommend taking the train. The airport express goes every 10 minutes to the city centre and every 20 minutes to Oslo West. If you get off at Oslo S (S=sentral stasjon) - a 20 minute ride from the airport - you can take a taxi to the terminal, or public transportation.
I would not recommend the bus (takes to long) - or a taxi (unless there are a lot of you). Both of these take considerably longer.
The train costs NOK 160 pp, the cheapest taxi is Taxi2 if you book it inside the terminal and costs NOK 440.
Thank you to you both for your answers. It's sure to help me to make plan for our forthcoming trip.