| Országos Kamaraszínház | Országos Kamaraszínház | Hungary, Mezőtúr | 1925-09-23 | -- | 1925–1927 | 2 | |
| Orpheum | Orpheum | Germany, Munich | 1893-03-08 | -- | 1893–1895 | 3 | |
| Opera House | Opera House | United States, Wyoming, Wyoming | -- | -- | | | |
| Otto-Klenert-Schule | Otto-Klenert-Schule | Germany, Bad Friedrichshall, Rathausplatz 7 | 2006-02-18 | -- | 2006 | 1 | |
| Osnabrücker Hof | Osnabrücker Hof | Germany, Osnabrück, Kollegienwall 14 | 1896-05-13 | -- | 1896 | 1 | |
| O'Connell Theatre | O'Connell Theatre | United States, Dekalb, Stevens Building, School of Theatre and Dance Northern Illinois University | 2009-02-19 | 2009-03-01 | 2009 | 1 | |
| Olomouc | Olomouc | Czech Republic, Olomouc | 2007-05-17 | -- | 2007 | 1 | |
| Orange Tree Theatre, The | The Orange Tree Theatre | England, London, 1 Clarence St, Richmond | 1991-10-10 | 2012-12-15 | 1991–2012 | 3 | |
| Orosháza | Orosháza | Hungary, Orosháza | 1890-05-12 | -- | 1890–1926 | 6 | |
| Operetten Neues Theater, Central Theater | Operetten Neues Theater, Central Theater | Germany, Leipzig | 1910-08-23 | 1910-08-30 | 1910 | 1 | |
| Osobnyak Theatre | Osobnyak Theatre | Russia, St. Petersburg, Kamennoostrovsky 55 | 2011-05-15 | 2011-05-17 | 2011 | 1 | |
| Östgötateatern | Östgötateatern | Sweden, Norrköping, Slottsgatan 135 | 1997-11-15 | -- | 1997 | 1 | |
| Opera Națională București | Opera Națională București | Romania, Bucharest, Bulevardul Mihail Kogălniceanu 70-72 | 2007-05-09 | -- | 2007 | 1 | |
| Ohgawara | Ohgawara | Japan, Ohgawara | 2010-02-02 | -- | 2010 | 1 | |
| Ontmoetingscentrum Aalbeke | Ontmoetingscentrum Aalbeke | Belgium, Aalbeke, Aalbekeplaats | 2001-03-12 | 2001-03-12 | 2001 | 1 | |
| Ontmoetingscentrum 't Waaigat | Ontmoetingscentrum 't Waaigat | Belgium, Zwijndrecht, Kerkplein 1 | 2003-05-06 | 2003-05-06 | 2003 | 1 | |
| Oravais Teater | Oravais Teater | Finland, Kimo, Oravais, Kyroboas Kvarn | 1996-07-11 | -- | 1996 | 1 | |
| Opernhaus | Opernhaus | Germany, Essen | 1942-04-19 | -- | 1942 | 1 | |
| Opera House | Opera House | United States, Pensacola | 1903-10-25 | 1903-10-25 | 1903 | 1 | |
| Oakland University | Oakland University | United States, Rochester, 2200 North Squirrel Road | 1972-03-02 | 1972-03-26 | 1972 | 1 | |
| Orkdal Samfunnshus | Orkdal Samfunnshus | Norway, Fannrem | 1978-11-22 | -- | 1978 | 1 | |
| Overture Center for the Arts, The Playhouse | Overture Center for the Arts, The Playhouse | United States, Madison, 201 State St | 2010-03-18 | 2010-03-28 | 2010 | 1 | |
| Opera House | Opera House | United States, Concord | 1909-04-22 | 1909-04-22 | 1909 | 1 | |
| Opština Bečej | Opština Bečej | Serbia, Opština Bečej | 1903-03-11 | -- | 1903 | 1 | |
| Ouagadougou, Carrefour Internationale de Théâtre de Ouagadougou | Carrefour Internationale de Théâtre de Ouagadougou | Burkina Faso, Bilbalogho, Ouagadougou, Burkina Faso | 2002-07-13 | -- | 2002 | 1 | |
| Odder Theater | Odder Theater | Denmark, Odder | 1905-11-25 | -- | 1905–1907 | 4 | |
| OSCO - Open Space Hannover | OSCO - Open Space Hannover | Germany, Hannover, Fössestraße 103 | 2019-11-14 | 2019-11-17 | 2019 | 1 | |
| OBOS-gården Wesselsgate 15 | OBOS-gården Wesselsgate 15 | Norway, Oslo, Museumsveien 10 | 2006-05-20 | 2008-06-13 | 2006–2008 | 2 | |
| Obergrafschaft, Theater der | Theater der Obergrafschaft | Germany, Schüttorf, Hermann-Schlikker-Str. 1-3 | 2015-10-03 | -- | 2015 | 1 | |
| Oerlenbach | Oerlenbach | Germany, Oerlenbach | 2009-12-19 | -- | 2009 | 1 | |
| Olathe Opera House | Olathe Opera House | United States, Olathe | 1908-01-31 | 1908-01-31 | 1908 | 1 | |
| Oravice | Oravice | Slovak Republic, Oravice | -- | -- | | | |
| Olofström | Olofström | Sweden, Olofström | 1992-11-12 | -- | 1992 | 1 | |
| Oslo Nye Dukketeater | Oslo Nye Dukketeater | Norway, Oslo, Rosenkrantz' gate 10 | 1994-08-23 | -- | 1994 | 1 | |
| Oblastnoi dramatičeskij teatr | Oblastnoi dramatičeskij teatr | Russia, Veliky Novgorod | 1948-09- | -- | 1948 | 1 | |
| Oldenburgisches Staatstheater | Oldenburgisches Staatstheater | Germany, Oldenburg, Theaterwall 28 | 1918-11-30 | 2015-12-20 | 1918–2015 | 12 | |
| Orkanger gymnas | Orkanger gymnas | Norway, Orkanger | 1970-02-13 | -- | 1970 | 1 | |
| Old Courthouse | Old Courthouse | Northern Ireland, Antrim, Market Square | 2011-05-26 | -- | 2011 | 1 | |
| O'Reilly Theatre | O'Reilly Theatre | Ireland, Dublin, Great Denmark Street | 2011-09-27 | 2011-10-16 | 2011 | 1 | |
| Opéra de Rouen | Opéra de Rouen | France, Rouen, 7 rue du Docteur Rambert | 2003-11-29 | 2003-11-30 | 2003 | 1 | |
| Odense Theater | Odense Theater | Denmark, Odense, Sortebrødre Torv | 1876-04-20 | 1899-10-20 | 1876–1901 | 9 | |
| Ovågen | Ovågen | Norway, Øygarden | 2005-09-04 | -- | 2005 | 1 | |
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