Now that I research it a bit (train to city and then pick up from Oslo the next morning would be ideal) - there are no locations open on Sunday before Noon - and we want to get an early start to enjoy the drive - say 8AM. So we might be stuck picking up Saturday night at the airport or downtown and pay for parking (unless we potentially park the car, while still under our possession, on Avis property for "free" parking). I used to this in Geneva when I lived next door to an Avis.