Nor-Way Bussekspress operates a bus from Oslo to Skien every 3 hours. Tickets cost $20 and the journey takes 2 h 5 min. Alternatively, Norwegian Railways (NSB) operates a train from Oslo to Skien hourly. Tickets cost $24 - $35 and the journey takes 2 h 40 min. 4 other operators also service this route.
From Oslo Bussterminal bus to Rådhusplassen. 2 h 5 min kr 159. From Oslo S train to Skien stasjon [buss] then bus to Skien terminal Landmannstorget. 2 h 47 min kr 309. From Oslo drive to Skien. 1 h 52 min kr 227.