The Østensjø Line (Norwegian: Østensjøbanen) is a 9.0-kilometre (5.6 mi) line on the Oslo Metro which runs from Brynseng to Mortensrud. It further shares track with the Lambertseter Line along the 2.5-kilometre (1.6 mi) section from Tøyen to Brynseng. The line runs through the primary residential areas of Bøler, Østensjø and Søndre Nordstrand. The line is served by Line 3 of the metro.