A/S Bærumsbanen was a tram company that operated the Lillaker-, Kolsås and Østensjø Line of the Oslo Tramway, Norway, from 1924 to 1971 when the company became part of Oslo Sporveier.

The final part of the Skøyen Line, from Skøyen to Lillaker was a suburban tramway located in the neighboring municipality of Aker, and the Municipality of Oslo was not interested in taking over it.

[1] The new company immediately started expanding the Lilleaker Line, first to Bekkestua and then to Haslum—establishing a depot at Avløs at the same time.

This opened on 15 June 1942—at the same time the Oppsal route was limited to running to Jar.

[1] On 1 October 1944 Oslo Sporveier bought the whole company, but not until 1 July 1971 did they fully merge.