Police confirmed that the victim died at Ullevål hospital shortly after he was shot at a Shell station in the Ensjø district at 10.15pm.
All available police resources were deployed in the search for a silver-grey Skoda station wagon seen leaving the scene, but there were no arrests in the case by Tuesday morning.
The shooting is thought to have been gang-related, newspaper VG reports.
Police officers who happened to be in the area at the time said they heard a shot and drove immediately to the petrol station.
”They heard something that sounded like a shot,” said police investigator Arve Røtterud, adding that the officers heard two more shots on arrival at the scene.
There is strong evidence to suggest that shots were fired both inside and outside the petrol station, Røtterud said.