| Old Fire Station Studio Theatre | Old Fire Station Studio Theatre | England, Oxford, 40 George St | 2003-11-11 | 2018-10-06 | 2003–2018 | 2 | |
| Ostróg | Ostróg | Poland, Ostróg | -- | -- | | | |
| O'Reilly Theatre | O'Reilly Theatre | Ireland, Dublin, Great Denmark Street | 2011-09-27 | 2011-10-16 | 2011 | 1 | |
| Opera House | Opera House | United States of America, New Castle | 1904-04-29 | 1908-04-11 | 1904–1908 | 2 | |
| Oerol Festival | Oerol Festival | Netherlands, Terschelling | 2014-06-13 | 2016-06-18 | 2014–2016 | 2 | |
| Östersund | Östersund | Sweden, Östersund | 1879-- | -- | 1879 | 1 | |
| Opéra de Dijon | Opéra de Dijon | France, Dijon, 11 Boulevard de Verdun | 2014-03-10 | 2014-03-12 | 2014 | 1 | |
| Operetten Neues Theater, Central Theater | Operetten Neues Theater, Central Theater | Germany, Leipzig | 1910-08-23 | 1910-08-30 | 1910 | 1 | |
| Oslo Nye teater | Oslo Nye Teater (Hovedscenen) | Norway, Oslo, Rosenkrantz' gate 10, Oslo, Norway | 2023-06-08 | 2023-08-24 | 2023 | 1 | |
| Ocean Hotell | Ocean Hotell | Norway, Horten, Jernbanegata 1 | 2006-02-02 | -- | 2006 | 1 | |
| Olomouc | Olomouc | Czech Republic, Olomouc | 2007-05-17 | -- | 2007 | 1 | |
| Optima Playhouse | Optima Playhouse | Australia, Adelaide, Festival Drive | 1999-07-06 | 1999-07-24 | 1999 | 1 | |
| Obârşia | Obârşia | Romania, Obârşia | -- | -- | | | |
| Overture Center for the Arts, The Playhouse | Overture Center for the Arts, The Playhouse | United States of America, Madison, 201 State St | 2010-03-18 | 2010-03-28 | 2010 | 1 | |
| Ottumwa | Ottumwa | United States of America, Ottumwa | 1903-11-04 | 1903-11-04 | 1903 | 1 | |
| Oxford Playhouse | Oxford Playhouse | England, Oxford, 11-12 Beaumont Street | 1924-05-05 | 2018-02-24 | 1924–2018 | 21 | |
| Odsherred Teater | Odsherred Teater | Denmark, Nykobing Sjaelland, Annebergparken 22 | 2002-02-27 | -- | 2002–2006 | 2 | |
| Opera House | Opera House | United States of America, Pensacola | 1903-10-25 | 1903-10-25 | 1903 | 1 | |
| Örebro Teater | Örebro Teater | Sweden, Örebro, Storgatan 1 | 1876-09-23 | 1889-12-14 | 1876–1909 | 8 | |
| Operahuset Nordfjord | Operahuset Nordfjord | Norway, Nordfjord, Sophus Lie-vegen 3 | 2009-11-09 | -- | 2009–2017 | 6 | |
| Opern- und Schauspielhaus Hannover | Opern- und Schauspielhaus Hannover | Germany, Hannover | 1920-06-21 | -- | 1920–1924 | 2 | |
| Orange Tree Theatre, The | The Orange Tree Theatre | England, London, 1 Clarence St, Richmond | 1991-10-10 | 2012-12-15 | 1991–2012 | 3 | |
| Ottawa Little Theatre Group | Ottawa Little Theatre Group | Canada, Ottawa | 1945-12-20 | -- | 1945 | 1 | |
| Old globe theatre, the | The Old Globe Theatre | United States of America, San Diego, 1363 Old Globe Way | 1995-04-30 | 1995-06-18 | 1995 | 1 | |
| Opera Națională București | Opera Națională București | Romania, Bucharest, Bulevardul Mihail Kogălniceanu 70-72 | 2007-05-09 | -- | 2007 | 1 | |
| Oddfellows' Hall | Oddfellows' Hall | Australia, Wagga Wagga, Fitzmaurice Street | -- | -- | | | |
| Oblastnoi dramteatr Volgograd | Oblastnoi dramteatr Volgograd | Russia, Volgograd | 1948-10- | -- | 1948 | 1 | |
| Opole | Opole | Poland, Opole | -- | -- | | | |
| Országos Kamaraszínház | Országos Kamaraszínház | Hungary, Mezőtúr | 1925-09-23 | -- | 1925–1927 | 2 | |
| Opera House | Opera House | United States of America, Bemidji | 1904-09-20 | 1904-09-20 | 1904 | 1 | |
| Odensbacken | Odensbacken | Sweden | 2002-09-12 | -- | 2002 | 1 | |
| Olivier Theatre | Olivier Theatre | England, Southbank, London, National Theatre, Upper Ground | 1978-04-25 | 2019-10-08 | 1978–2019 | 11 | |
| Ocna Sibiului | Ocna Sibiului | Romania, Ocna Sibiului | -- | -- | | | |
| Opera House | Opera House | United States of America, Santa Cruz | 1905-07-28 | 1905-07-28 | 1905 | 1 | |
| Opera House | Opera House | England, Coventry, 4 Hales Street | 1911-09-11 | 1911-09-14 | 1911 | 1 | |
| Opernhaus | Opernhaus | Germany, Wuppertal, Kurt-Drees-Straße 4 | 2011-06-26 | 2011-12-01 | 2011 | 2 | |
| Onde, L' | L'Onde | France, Vélizy-Villacoublay, 8 bis Avenue Louis Breguet | 2015-05-19 | 2018-01-19 | 2015–2018 | 2 | |
| Opernhaus | Opernhaus | Germany, Frankfurt, Opernplatz 1 | 1892-12-10 | -- | 1892–1940 | 2 | |
| Opéra National de Lyon | Opéra National de Lyon | France, Lyon, 1 place de la Comédie | 2022-06-04 | 2022-06-13 | 2022 | 1 | |
| Omskiy Gosudarstvennyy Dramaticheskiy Pyatyy Teatr | Omskiy Gosudarstvennyy Dramaticheskiy Pyatyy Teatr | Russia, Omsk, ul. Krasnyy Put' 153 | 2005-10-01 | -- | 2005 | 1 | |
| Old Town Hall Arts Center | Old Town Hall Arts Center | England, Hertfordshire, Hemel Hempstead | 1985-02-18 | 1985-02-20 | 1985–2011 | 2 | |
| Opéra National de Lorraine | Opéra National de Lorraine | France, Nancy, 1 Rue Sainte-Catherine, | 2013-05-23 | -- | 2013 | 1 | |
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