| Oslo Nye Teater (Centralteatret) | Oslo Nye Teater (Centralteatret) | Norway, Oslo, Akersgata 38 | 1972-09-28 | 2017-06-17 | 1972–2017 | 10 | |
| Överkalix Folkets Hus | Överkalix Folkets Hus | Sweden, Överkalix, Bulandsgatan 2 | 2010-11-16 | -- | 2010 | 1 | |
| Oxford Playhouse | Oxford Playhouse | England, Oxford, 11-12 Beaumont Street | 1924-05-05 | 2018-02-24 | 1924–2018 | 21 | |
| Odeon-Theater | Odeon-Theater | Germany, Goslar, Bismarckstraße 1 | 1997-10-10 | 1997-10-10 | 1997–2005 | 2 | |
| Oslo Public Library | Oslo Public Library | Norway, Oslo, Arne Garborgs plass 4 | 1988-06-30 | -- | 1988 | 1 | |
| Opera Theatre | Opera Theatre | France, Limoges, 48, Rue Jean-jaurès | 2017-05-09 | 2017-05-11 | 2017 | 1 | |
| Opernhaus Chemnitz | Opernhaus Chemnitz | Germany, Chemnitz, Theaterstraße 2 | 1927-09-27 | -- | 1927–1991 | 4 | |
| Opera House | Opera House | United States, McCook | 1905-03-16 | 1905-03-16 | 1905 | 1 | |
| Orosháza | Orosháza | Hungary, Orosháza | 1890-05-12 | -- | 1890–1926 | 6 | |
| Ophelia Theater | Ophelia Theater | United States, Astoria, 21-12 30th Road | 2016-10-28 | 2016-11-13 | 2016 | 1 | |
| Otta kulturhus | Otta kulturhus | Norway, Otta, Skansen 9 | 1993-03-07 | 2018-09-08 | 1993–2018 | 13 | |
| Opera House | Opera House | United States, San Bernardino | 1903-12-31 | 1908-12-04 | 1903–1908 | 2 | |
| Ovalhouse | Ovalhouse | England, London, 52-54 Kennington Oval | 2018-05-17 | 2018-05-19 | 2018 | 1 | |
| Origosenteret | Origosenteret | Norway, Svinndal, Tyritoppen 19 | 2012-11-26 | -- | 2012 | 2 | |
| O'Reilly Theatre | O'Reilly Theatre | Ireland, Dublin, Great Denmark Street | 2011-09-27 | 2011-10-16 | 2011 | 1 | |
| Old Auditorium, Worcester State College | Old Auditorium, Worcester State College | United States, Worcester, 486 Chandler Street | 1971-04-29 | 1971-05-01 | 1971 | 1 | |
| Ornans | Ornans | France, Ornans | 2001-- | -- | 2001 | 1 | |
| Oblasni dram teatr | Oblasni dram teatr | Russia, Kaliningrad, Prospekt Mira, 4 | 1960-01- | -- | 1960–1973 | 2 | |
| Old Tote Theatre, The | The Old Tote Theatre | Australia, Kensington, High Street | 1967-09-23 | 1971-08-03 | 1967–1971 | 2 | |
| Obârşia | Obârşia | Romania, Obârşia | -- | -- | | | |
| Otta | Otta | Norway, Otta | 1971-03-19 | -- | 1971–2004 | 4 | |
| OPERATTEN im STATTtheater | OPERATTEN im STATTtheater | Switzerland, Stäfa, Bahnhofstrasse 52 | 2007-03-07 | 2007-04-21 | 2007 | 1 | |
| Orăștie | Orăștie | Romania, Orăștie | 1911-02-16 | -- | 1911 | 1 | |
| Omaha | Omaha | United States, Omaha | 1903-11-05 | 1903-11-05 | 1903 | 1 | |
| Oscarsborg Festning | Oscarsborg Festning | Norway, Oscarsborg, Husvikveien | 2006-07-27 | 2007-06-24 | 2006–2007 | 2 | |
| Opera House | Opera House | United States, New Castle | 1907-03-09 | 1907-03-09 | 1907 | 1 | |
| Ostróg | Ostróg | Poland, Ostróg | -- | -- | | | |
| Old Red Lion Theatre | Old Red Lion Theatre | England, London, 418 St John Street | 2000-10-17 | 2000-11-11 | 2000 | 1 | |
| Old Town Players | Old Town Players | United States, Chicago | 1973-02-09 | 1973-04-15 | 1973 | 1 | |
| OC Vondel (Ontmoetingscentrum Meulebeke) | OC Vondel (Ontmoetingscentrum Meulebeke) | Belgium, Meulebeke, Karel van Manderstraat 26 | 2002-02-28 | 2002-02-28 | 2002 | 1 | |
| Otto-Klenert-Schule | Otto-Klenert-Schule | Germany, Bad Friedrichshall, Rathausplatz 7 | 2006-02-18 | -- | 2006 | 1 | |
| Optima Playhouse | Optima Playhouse | Australia, Adelaide, Festival Drive | 1999-07-06 | 1999-07-24 | 1999 | 1 | |
| Odin Teatret | Odin Teatret | Denmark, Holstebro, Særkærparken 144 | 2011-- | -- | 2011–2016 | 4 | |
| Orpheum | Orpheum | Germany, Munich | 1893-03-08 | -- | 1893–1895 | 3 | |
| Olathe Opera House | Olathe Opera House | United States, Olathe | 1908-01-31 | 1908-01-31 | 1908 | 1 | |
| Odeon | Odeon | Argentina, Buenos Aires | 1904-06-24 | 1904-06-26 | 1904 | 1 | |
| Olympic Theatre | Olympic Theatre | United States, St. Louis | 1891-01-11 | 1910-04-03 | 1891–1910 | 7 | |
| Osobnyak Theatre | Osobnyak Theatre | Russia, St. Petersburg, Kamennoostrovsky 55 | 2011-05-15 | 2011-05-17 | 2011 | 1 | |
| Operahuset Nordfjord | Operahuset Nordfjord | Norway, Nordfjord, Sophus Lie-vegen 3 | 2009-11-09 | -- | 2009–2017 | 6 | |
| Ocna Sibiului | Ocna Sibiului | Romania, Ocna Sibiului | -- | -- | | | |
| Octagon, The | The Octagon | United States, Montgomery, 1 Festival Drive | 1997-03-04 | 2002-04-14 | 1997–2002 | 2 | |
| Ohkuma Auditorium | Ohkuma Auditorium | Japan, Tokyo, Japan | 1954-09-11 | -- | 1954–1965 | 3 | |
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