So why was the airport placed here? Yes, because as early as 1927, the island of Gressholmen had served as Oslo's main seaplane airport, but it was impractical to transport everyone out by boat and eventually there was a conflict with boat traffic.Various alternatives were considered and they landed at Fornebu, because there it was possible to combine an airport for land and seaplanes. There was a lot of unemployment in the 1930s, and permission was therefore granted for development in 1935. Initially, 3 runways were built, but only the north-south runway became important for traffic flow and the others were closed down after the war.

The airport was occupied by the Germans during World War II, and civil air traffic was suspended between 1940 and 1946. West of the airport, at Oksenøya farm, the Germans set up a prison camp. One of the prisoners' tasks in the winter was to keep the runways clear of snow, and by marching they trampled the snow so that the planes could use the runways.

The main users of the airport were Braathens SAFE (South American and Far East Air Transport) and SAS. The first long-haul flights were only carried out during the day because the planes' range and top speed were so low compared to today that the routes had to be divided into several sections, so that the crew could rest between each flight. The first Braathens SAFE flights between Oslo and Hong Kong for example were set up with stops in Amsterdam, Marseille, Cairo, Basra, Karachi, Calcutta and Bangkok in that order. At the time, the route was the world's longest continuous flight route. The airline that flew the longest at Fornebu was Dutch KLM; the company participated in the opening on 1 June 1939 and, with the exception of the war years, they flew continuously until the airport was closed.

In the post-war period, there were several step-by-step expansions of both terminals and runways, and Fornebu was the workplace for over 5,000 people in the early 90s. As a passenger, it is easy to overlook that an airport is more than planes and airlines. These services were also necessary to keep the airport running: air traffic controllers, weather service, fire and rescue service, customs, freight, mail, fuel suppliers, police, security and various types of service personnel. From a modest beginning with a few departures per today, the number of travelers reached 10 million in 1997 before the move to Gardermoen.

As a central area with proximity to Oslo, it also helped to build up the local environment with a rich working life and large influx of people. Today, the area is being developed into "Fornebyen", a city, trade and residential area. Today, seaplanes are allowed to operate in Lilløykilen through Kilen Sjøflyklubb.