| Opera House | Opera House | United States of America, New Castle | 1904-04-29 | 1908-04-11 | 1904–1908 | 2 | |
| Opera Comique Theatre | Opera Comique Theatre | England, London | 1889-07-17 | 1895-03-30 | 1889–1895 | 6 | |
| Oravais Teater | Oravais Teater | Finland, Kimo, Oravais, Kyroboas Kvarn | 1996-07-11 | -- | 1996 | 1 | |
| Olde Towne Hall Theatre | Olde Towne Hall Theatre | United States of America, North Ridgeville, 36119 Center Ridge Road | 2018-05-18 | 2018-05-19 | 2018 | 1 | |
| Old Rep at Birmingham Repertory Theatre | The Old Rep at Birmingham Repertory Theatre | England, Birmingham | 2013-03-14 | 2013-03-28 | 2013 | 1 | |
| Old Fire Station Studio Theatre | Old Fire Station Studio Theatre | England, Oxford, 40 George St | 2003-11-11 | 2018-10-06 | 2003–2018 | 2 | |
| Orikkusu Gekijō | Orikkusu Gekijō (Orix Theater) | Japan, Osaka, 1-14-15 Shin-machi, Nishi-ku | 1971-10-03 | -- | 1971 | 2 | |
| Old Vic, The | The Old Vic | England, London, The Cut | 1922-03-06 | 2016-03-19 | 1922–2016 | 11 | |
| ORF Radio (Austria) | ORF Radio (Austria) | Austria | 1991-04-18 | -- | 1991 | 1 | |
| Oosterpoort Groningen, De | De Oosterpoort Groningen | Netherlands, 9724 DA, Trompsingel 27, | 2000-04-20 | 2000-04-21 | 2000 | 1 | |
| Olomouc | Olomouc | Czech Republic, Olomouc | 2007-05-17 | -- | 2007 | 1 | |
| Oakland University | Oakland University | United States of America, Rochester, 2200 North Squirrel Road | 1972-03-02 | 1972-03-26 | 1972 | 1 | |
| Olofström | Olofström | Sweden, Olofström | 1992-11-12 | -- | 1992 | 1 | |
| Oliver Theatre | Oliver Theatre | United States of America, Lincoln | 1903-05-09 | 1908-11-03 | 1903–1908 | 2 | |
| 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 | |
| Opernhaus Hannover | Opernhaus Hannover | Germany, Hannover, Opernplatz 1 | 1928-03-06 | 1956-12-05 | 1928–1956 | 2 | |
| Oblastnoj teatr dramy | Oblastnoj teatr dramy | Russia, Čeljabinsk | 1978-09- | -- | 1978 | 1 | |
| Oriental Vevey | Oriental Vevey | Switzerland, Vevey, Rue d'Italie, 22 | 2018-10-31 | 2018-11-18 | 2018 | 2 | |
| Opera House | Opera House | United States of America, Kentucky, Kentucky | 1899-12-20 | 1903-12-10 | 1899–1903 | 2 | |
| Opern- und Schauspielhaus Hannover | Opern- und Schauspielhaus Hannover | Germany, Hannover | 1920-06-21 | -- | 1920–1924 | 2 | |
| Oldenburgisches Staatstheater | Oldenburgisches Staatstheater | Germany, Oldenburg, Theaterwall 28 | 1918-11-30 | 2015-12-20 | 1918–2015 | 12 | |
| Oberlin College & Conservatory, Hall auditorium | Oberlin College & Conservatory | United States of America, Oberlin, 67 North Main St. | 2014-04-17 | 2014-04-19 | 2014 | 1 | |
| Oslo Nye Dukketeater | Oslo Nye Dukketeater | Norway, Oslo | 1994-08-23 | -- | 1994 | 1 | |
| Opole | Opole | Poland, Opole | -- | -- | | | |
| Orfeó Gracienc | Orfeó Gracienc | Spain, Barcelona, Carrer d'Astúries, 83 (Gràcia) | 1910-07- | -- | 1910–1915 | 2 | |
| Olavskapellet, Borgarsyssel Museum | Olavskapellet, Borgarsyssel Museum | Norway, Sarpsborg, Gamlebygaten 8 | 2006-08-01 | 2006-08-02 | 2006 | 1 | |
| Osservatorio, Teatro | Teatro Osservatorio | Italy, Bari, Trento 12 | 2017-05-07 | -- | 2017 | 1 | |
| Opera House | Opera House | United States of America, Bemidji | 1904-09-20 | 1904-09-20 | 1904 | 1 | |
| Odense | Odense | Denmark, Odense | 1948-04-20 | -- | 1948–2000 | 2 | |
| Osimo | Osimo | Italy | -- | -- | | | |
| Ocna Mureș | Ocna Mureș | Romania, Ocna Mureș | 1890-02-06 | -- | 1890–1911 | 2 | |
| Orpheum | Orpheum | United States of America, El Paso | 1908-06-18 | 1908-06-18 | 1908 | 1 | |
| Opernzelt | Opernzelt | Germany, Heidelberg, Emil-Maier-Straße 16 | 2011-04-29 | 2011-07-05 | 2011 | 1 | |
| Odensbacken | Odensbacken | Sweden | 2002-09-12 | -- | 2002 | 1 | |
| Oseana Kunst & Kultursenter | Oseana Kunst & Kultursenter | Norway, Os, Mobergsbakken 20 | 2012-09-18 | 2020-09-13 | 2012–2020 | 5 | |
| Orkanger gymnas | Orkanger gymnas | Norway, Orkanger | 1970-02-13 | -- | 1970 | 1 | |
| Opera House | Opera House | United States of America, Santa Cruz | 1905-07-28 | 1905-07-28 | 1905 | 1 | |
| Ohio State University | Ohio State University | United States of America, Columbus, 1739 North High Street | 1981-02-27 | 2001-03-04 | 1981–2001 | 2 | |
| Oppdal | Oppdal | Norway, Oppdal | -- | -- | | | |
| Oslo Domkirke | Oslo Domkirke | Norway, Oslo, Karl Johans gate 11 | 2018-02-09 | 2018-02-10 | 2018 | 1 | |
| Odd Duck Studio | Odd Duck Studio | United States of America, Seattle, 1214 10th Avenue | 2008-11-26 | 2008-12-20 | 2008 | 1 | |
| Opéra-Théâtre i Avignon | Opéra-Théâtre i Avignon | France, Avignon, 1 Rue Racine | 2012-07-18 | 2012-07-25 | 2012 | 1 | |
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