The network consists of five lines that all run through the city centre, with a total length of 85 kilometres (53 mi),[2] serving 101 stations of which 17 are underground or indoors.

In addition to serving 14 out of the 15 boroughs of Oslo, two lines run to Kolsås and Østerås, in the neighbouring municipality of Bærum.

After 1993 trains ran under the city between the eastern and western networks in the Common Tunnel, followed by the 2006 opening of the Ring Line.

Rail transport in Oslo started in 1854, with the opening of Hoved Line to Eidsvoll, through Groruddalen.

[13][14] This service remained part of the municipal Oslo Sporveier, that had bought all the streetcar companies in 1924.

[10] The first idea to launch a citywide rapid transit was launched in 1912 with the construction of the Ekeberg Line; constructed with the same width profile as the Holmenkollen Line, the plan was to build a tunnel under the city center and run through trains, but large cost expenditures on the first section of the Common Tunnel ceased the plans.

The system would feature improvements over the suburban lines in having a third rail power supply, cab signaling with Automatic Train Protection, stations long enough for six-car trains and level crossings replaced by bridges and underpasses—specifications christened metro standard.

[18] The metro took delivery of T1000 rolling stock from Strømmens Værksted; from 1964 to 1978, 162 cars in three-car configurations were delivered for the eastern network.

This station was forced to close in 1983, due to water leakage, and when it opened again in 1987, renamed Stortinget, the west network tunnel had also been extended there.

[14] The following year, construction work caused a tunnel to collapse on the Grorud Line—the system's busiest—forcing a shutdown of the line until December, and creating a havoc of overcrowded replacement buses.

[25] Lines: The current route network was introduced on 3 April 2016, with the opening of the connection tunnel from Økern to Sinsen and the new Løren station.

[26] A new metro line that will extend from Majorstuen to Fornebu is under construction as of December 2020, aiming to be completed in 2027.

[40] The street trams operate mostly within the borders of the Ring Line, providing a frequent service in the city centre, with lower average speeds but with more stops.

There are major transfer points to the tramway at Majorstuen, Jernbanetorget, Jar, Storo and Forskningsparken.

Transfer to railway services is available at Jernbanetorget (to Oslo S) and Nationaltheatret, the latter with a considerably shorter walk.

Most bus services provide feeding to the metro system where possible, and then do not continue into town.

The trains on the Oslo metro are currently exclusively the MX3000, ordered in 2003 to replace the oldest T1000 stock.

Delivery started in 2006, and unlike older stock the MX3000 units are painted white instead of red.

This includes 146 cars of the types T1 through T4, that have third-rail only operation, and thus did not run on the Holmenkollen and Kolsås lines.

[21] When the Holmenkollen Line was connected to the T-bane it was still using old teak cars; to allow through services the T2000, capable of dual-system running, was delivered in 1993.