Hitching out of Oslo is difficult from the city center. There are several motorway entrances behind the tunnel. The further outside the city you are, the easier it gets.
North towards Trondheim
The trip to Trondheim takes one day.
Around IKEA (Furuset] is an area where most trucks start. There is a petrol station on the E6 direction North which can be reached walking from metro station "Trosterud", East of the centre (lines 1 or 2, direction Ellingsrudåsen). The metro in Oslo is called the T. From the stop Trosterud you go out, to the left, left again down the hill, over the footbridge and continue down and you are behind the station.
- abstorz was able to hitch a ride onto the motorway behind the tunnel in the area of Etterstad, but it can't be bad to get even further out of the city. Once on the motorway everything went fine.
If you want to go south-east on the E6 take metro line 3 to "Mortensrud" and get off at the last station, then cross the bridge over metro track and walk for about 300 meters. You will enter petrol station on motorway E6. Ask drivers there. Very good spot! (Update: as of September 2012, the station is under some kind of construction but the market is still open. I was worried there wouldn't be any traffic but people do still stop for the market. I took a short hitch to one of the next exits down the highway with a gas station and McDonalds though, and that worked out to Goteburg - that ride was actually going all the way to Copenhagen.)
You can also take the regional train going "Ski" and get off at "Nordstrand" station, one stop after Oslo-S. Once at Nordstrand, turn left and go down the little hill. The large road with a lot of traffic is the E18. You can walk about 5-10 minutes in the direction of Oslo (turning right) to the Ulvøya Island crossroad. There is a bus stop right after a traffic light and you can get picked up quite easily. Have a sign and avoid anyone going in the direction of Stockholm.
Alternatively you may want to try Esso gas station (diesel is cheaper there so lots of people fills up there and other advantage is there is a MC D. right next to it). To get there, take subway to Hellerud, turn right into Smalvollveien and walk till you get to Esso. Some might find useful to know that there seem to be fewer ticket controls on that line.
West towards Bergen
To get to Bergen, take the local train out to "Sandvika", from where you can either take a bus or walk along the road (quite a few k's) until it turns from dual carriageway to a simple country road, where you can just hitch along the side.
Alternatively take the train to "Honefoss", walk up the hill and out to the road, and there is an information point where it's easy for drivers to pull in- all traffic from Oslo to Bergen goes past this point.
Hitchhiking from Oslo to Bergen can be pretty challenging in winter.I have tried from west of Oslo and without any luck I turned to the area where the goods terminals located.It is in the north east side of the city.Keep in mind most of the trucks are using RV 7 to go to Bergen and try to avoid being left at the small towns like Gol,Hemsedal which can prove very hard to get out of. If you want to cover a long distance by a truck your best chance to get a truck to your destination from Schenker Goods Terminal near Alna Senter.From the central station you can eighter take subway to Tveita Metro stop and walk across the E6 by Ytre Ringvei or take the train to Alna.You will not miss huge Schenker sign board.It is forbidden to enter the terminal area so wait outside the gate at the Alnabruveien and Terminalveien with a sign of your destination,by doing this you would also catch up a ride by Tollpost Globe ASs trucks.The trucks continues on Alnabruveien keeps eighter on the E6 South,E18 West or E16.Trucks leaving for E6 north turn into Terminalveien.
From Oslo (Rygge) Airport
Oslo (Rygge) is an airport located about 75 km South of Oslo, on the E6 direction Göteborg. To reach Oslo via HH, you simple need a sign for Oslo and you can either hitch from the airport or walk about 1,5 km to (North direction, along the motorway) the Rygge on-ramp where local traffic passes at the roundabout. The first petrol station is a few kilometres North, around Moss. From there it's rather easy to get a direct ride to Oslo.
Yes, the airport is small, so traffic is light. When you come out of the terminal building; the motorway in front of you is the E6, and Oslo (North) is to the right. I walked the one mile along the airport service road (hitching without success)and then hitched from the roundabout.
Or you can just stand at the end of the car park building on the slip road (turn right out of terminal building and walk til you reach the end of the building). I just hitched to Oslo city centre in one lift (by holding up an 'Oslo' sign). The first car stopped. Or you can ask people at the airport if they're going to Oslo. My brother did this and got a lift with the first person he asked.
I was heading East to Töcksfors (just over the Swedish border on the E18) so got dropped at the junction of the 151 near the town of Son and continued East from there. Not the easiest hitch (4 hours) but still much quicker than getting the airport bus into Oslo and then the Stockholm bus back out to Töcksfors. I found drivers friendly, willing to go a little out of their way, and everyone spoke good English.
From Oslo (Torp) Airport
The ticket is 26 kr. Note that you can buy it on the train (for 40 kr if you buy it from a person instead of the machine) and they might not check, but it's almost impossible to dodge on regional trains.
At least one hitchhiker rode for more than a week on bus, tram and subway without ever buying a ticket. If you get busted, just choose to pay later, give a false address and you will never hear from them again.
Other Useful Info
Free luggage storage: There are free lockers in the main Oslo library if you want to store luggage for free (you need a ten kroner coin, which you'll get back after).
CAMPING: To the east of Oslo there is an extremely large and beautiful nature-reserve called Østmarka. The park has extensive hiking trails, numerous lakes with fishing and swimming, and a minimal amount of development. When I was there at the height of summer, it was never crowded if not almost completely deserted. Camping in the park is safe, free and legal and you could spend days exploring it. Best of all it's accessible from the T-bane and, thus, connected to downtown Oslo. Near the Trosterud station there's an entrance to the Lutvann Lake recreation area within the park. When you leave the station, follow the paved pedestrian road to the left just a few meters. There will be another paved road/bike path going up the hill to your right. Follow this all the way up. You will reach a cluster of apartment buildings. Keep following the asphalt path. It will end in a small parking lot and a raised basketball court I think. At this point turn right and follow the car-road. Turn left just past the basketball court and follow this road as it veers up and to the right, I think it's called Lutvannsveien. You will pass a military base and the entrance to the park is another 50 meters or so past that. The lake itself is another 5-10 minute walk inside the park, just follow the big gravel path. All told it's about a 20-30 minute hike from the station. For hitching this spot is ideal because it's also very close to the E6 going north. There's directions to hitching spots from Trosterud at the top of this page.wikitravel:Oslo