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O2, O-2, o2, O2, O2, O2− or O2+ may refer to:
Science and technology
- O2 or dioxygen, the common allotrope of the chemical element oxygen
- O2−, the ion oxide
- O−2, the ion superoxide
- O+2, the ion dioxygenyl
- O2+, doubly ionized oxygen
- O2, an EEG electrode site according to the 10–20 system
- SGI O2, a Unix workstation computer
- UOC O2, institutional repository of the Open University of Catalonia
- O2, the earliest defined spectral class for stars
Places
- The O2, an entertainment district in London, England
- The O2 Arena, the arena within The O2
- O2 Arena (Prague) or Sazka Arena, an arena in Prague, Czech Republic
- O2 Centre, an indoor shopping and entertainment centre on Finchley Road, London, England
- O2 Residence, a part of the Jumeirah Lake Towers in Dubai, United Arab Emirates
- O2 World (Berlin), an indoor arena in Berlin, Germany
- O2 World (Hamburg), an indoor arena in Hamburg, Germany
- Otoyol 2, a motorway in Turkey called "O2"
- The O2 (Dublin), the former name of 3Arena
- Ring 2 (Aarhus), a road in Aarhus, Denmark, which appears as "O2" on signs
- Ring 2 (Copenhagen), a road in Copenhagen, Denmark, which appears as "O2" on signs
Arts, entertainment, and media
Film
- Oxygen (2021 film) or O2, an American-French survival thriller film in production
- O2 (2020 film), an Estonian-Latvia-Lithuanian-Finnish historical spy thriller film
- O2 (2022 film), an Indian Tamil language survival thriller film
Music
Albums
- O2 (FireHouse album) (2000) album of the rock band FireHouse
- O2 (O-Town album) (2002) album by American boy band O-Town
- O2 (Tonéx album) (2002) album by Gospel singer Tonéx
- O2: Avalon Remixed, a 2002 album by Avalon
- O2 (Son of Dave album), 2006 album by Son of Dave
Songs
- "O2", a song by Orange Range from Panic Fancy
- "O2", a 2002 song by Sleater-Kinney from One Beat
- "O2", a song by Suho from Self-Portrait
Other arts, entertainment, and media
- Ö2, a radio service for Austria and South Tyrol
- O2, a character in Kirby 64: The Crystal Shards
Businesses and organisations
- O2, trading name for Telefónica Europe, a European telecommunications provider
- O2 Store, a chain of retail stores owned and operated by Telefónica Europe, with regional subsidiaries:
- O2 (brand), Telefónica mobile network global brand name
- O2 (Ireland), merged into Three Ireland
- O2 (UK)
- O2 Czech Republic
- Telefónica Germany
- Telefónica Slovakia
- O2 Academy, a chain of music venues
- O2 Wireless USA or H2O Wireless, a prepaid wireless service by Locus Telecommunications
- O2TV, a Russian independent socially political TV channel
Vehicles and vessels
- Cessna O-2 Skymaster, a military twin-engine light aircraft
- Douglas O-2, a military single-engine observation biplane
- O 2-class submarine, a class of submarines of the Royal Netherlands Navy
- Oldershaw O-2, a glider
- SP&S Class O-2, a 1910 steam locomotives class
- USS O-2 (SS-63), a 1918 United States O class submarine
- Orbital O2, a tidal power turbine in Orkney
- GNR Class O2, a class of British steam locomotives classified O2 by both the GNR and the LNER
Other uses
- O-2, a pay grade in the US uniformed services
- First lieutenant (United States) in the Army, Marine Corps, Air Force, and Space Force
- Lieutenant (junior grade) in the Navy, Coast Guard, Public Health Service Commissioned Corps, and NOAA Commissioned Officer Corps
