Ruter AS is the public transport authority for Oslo and Akershus counties in Norway. Formally a limited company – 60% of its shares are owned by the Oslo county municipality and 40% by that of Akershus – it is responsible for the administration, funding, and marketing (but not direct operation) of public transport in the two counties, including buses, the Oslo Metro (T-banen i Oslo), Oslo Trams (Trikken i Oslo), and ferry services. Ruter also holds agreements with Entur concerning the regulation of fares on local and regional train services operated within the two counties.

The operation of services is performed by other companies:

In 2011, 285 million journeys were made on the Ruter network. This is much more than the other regional public transport authorities together, and roughly half of the total number of public transport journeys in Norway together.^{[citation needed]}

Sporveien is an independent company wholly owned by the City of Oslo. It owns and maintains the rapid transit and tramway systems, including the rolling stock. The company was established on 1 July 2006, when the former Oslo Sporveier was split into an operating company and an administration company. The actual operation of the T-bane is performed by the subsidiary Sporveien T-banen, while the tramway is operated by Sporveien Trikken. Sporveien also owns Unibuss, which has won many of the public service obligation bids for bus operation in Oslo and Akershus. Unibuss also operates the coach service Lavprisekspressen.

Single, 1-day, 7-day, monthly, and yearly tickets are available. Ruter operates on a proof-of-payment system, and there is a fine of either NOK 950 or NOK 1,150 for traveling without a valid ticket, depending on whether or not the fine is paid on location. Payment is based on a zone fare schematic, and Oslo remains a single zone with free transfer. A single-zone ticket costs NOK 40 if bought in advance, and NOK 50 if bought on a bus or tram. Day passes cost NOK 121 while a month pass costs NOK 853. Children and seniors pay half price. Prices increase if multiple zones are traveled. The Flexus ticket system was introduced in 2011.

The Oslo Metro is the rapid transit system that serves all boroughs of Oslo, and also cuts deep into Bærum. It is operated by Oslo T-banedrift, a subsidiary of Kollektivtransportproduksjon. The network consists of five lines that all run through the city center, with a total length of 84.2 kilometres (52.3 mi). It has a daily ridership of 200,000 with 101 stations of which 16 are underground or indoors.

The first rapid transit line was the Holmenkoll Line, opened in 1898, with the branch Røa Line opening in 1912. It became the first Nordic underground railway in 1928 when the underground line to Nationaltheatret was opened. The Sognsvann Line opened in 1934 and the Kolsås Line in 1942. The opening of the upgraded metro network on the east side of town occurred in 1966, after the conversion of the 1957 Østensjø Line, followed by the new Lambertseter Line, the Grorud Line and the Furuset Line; in 1993 trains ran under the city between the two networks in the Common Tunnel, followed by the 2006 opening of the Ring Line. Between 2006 and 2010 the system is replacing the older T1000 stock with MX3000 stock.

The tramway (Norwegian: Trikken) consists of six lines running 131.4 kilometres (81.6 mi), with 99 stops and a daily ridership of 100,000—accounting for 20% of total public transport in Oslo. It is operated by Oslotrikken, a subsidiary of the municipal owned Kollektivtransportproduksjon, who maintain the track and 72 tram vehicles. The system operates on standard gauge and uses 750 volt direct current. Depot, workshops and headquarters are at Grefsen (at the terminus of lines 17 and 18).