Overall journey from the airport to the conference venue should take 1h 25min. For example to be at the hotel around lunch time one needs to depart from the Gardemoen airport at 10:43 the latest.
To reach Oslo city centre
Oslo city centre can be conveniently reached from the Oslo main airport Gardemoen via regular trains operated by NSB (departures from platform 4), and Flytoget or F2 (departures from platform 3). Tickets can be bought at the machines just in front of the corresponding platform. NSB ticket will cost ca. 101 NOK, while Flytoget 190 NOK. The journey will span from zone 4N to zone 1. Oslo S or "Jernbanetorget", central station and Nationaltheatret are the two stops where you can conveniently change to Oslo metro, called T-bane. Oslo S is a center hub for variety of buses and trams.
To reach Soria Moria
If you are travelling from the airport to Soria Moria hotel, at Oslo S or at the Nationaltheatret you can switch to metro (see the map above). Follow the direction for metro in the westbound direction and board metro line number 1 towards Frognerseteren. If facing the front of the train, seat on the left side of the compartment offers the best view over the Oslo fjord valley. For Soria Moria hotel you need to exit at Voksenkollen station (18 stops, 32 min from Nationaltheatret) and have ca. 1 km walk.
All Oslo is located within zone 1. If you need a ticket, ruter machines, labeled with a big # sign, sell them. Tickets are valid for all types of transport (train, bus, tram, Tbane, and a boat) for 1 hour or 24h. The same tickets can be bought at 7-eleven and Narvesen stores, scattered all over the city. Once you have a ticket it needs to be activated at the bus, tram or at the gates located at the entrance to a metro station.