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| Latest update: | 06-06-2023 |
Composers
O (37)
| Name | Born - Died | Place of birth | Requiems | |
 | Seán Ó Riada | 1931 - 1971 | Ireland | 1 |
| Anton Ulrich Obermayr | 18th - century | Austria | 2 | |
| Johann Obersteiner | 1824 - 1896 | Austria | 1 | |
| Jacob Obrecht | 1457/58 - 1505 | The Netherlands / Belgium | 2 |
| Oscar OBrien | 1892 - 1958 | Canada | 1 |
| Fergus OCarroll | 1956 - | Ireland | 1 |
| Tomás Ochando | 18th - century | Mexico | 3 | |
| Traugott Ochs | 1854 - 1919 | Germany | 1 | |
| Johannes Ockeghem | c.1420 - 1497 | The Netherlands / Belgium | 2 |
| Tomás ODrisceoil | 1986 - | Ireland | 1 |
| Helmut Oehring | 1961 - | Germany | 1 |
| Johann Lohelius Oelschlegel | 1724 - 1788 | Czech Republic | 1 |
| Bart Oenema | 1967 - | The Netherlands | 1 |
| Johannes Cornelis van Oers | 1860 - 1941 | The Netherlands | 1 |
| Rudolf von Oertzen | 1910 - 1990 | Germany | 1 |
| Joseph Ohnewald | 1781 - 1856 | Germany | 3 | |
| Hilario Olazaran de Estella | 1894 - 1963 | Spain | 2 |
| Juan Manuel Olivares | 1760 - 1797 | Venezuela | 4 |
| Domingo Olleta Mombiela | 1819 - 1890 | Spain | 1 |
| Otto Emanuel Olsson | 1879 - 1964 | Sweden | 1 |
| György Orbán | 1947 - | Rumania | Hungary | 2 |
| Conor OReilly | 1967 - | Ireland | 1 | |
| Joaquin Orellana Mejia | 1937 - | Guatemala | 1 |
| Carl Orff | 1895 - 1982 | Germany | 1 |
| Vincenzo Orgitano | c.1738 - aft.1815 | Italy | 1 | |
| Charles Wilfred Leslie Orr | 1893 - 1976 | Great Britain, England | 1 |
| Juan Antonio Orrego Salas | 1919 - 2019 | Chile | United States of America | 1 |
| Eduard Ortlieb | 1807 - 1861 | Germany | 1 |
| Clara Osmond | fl.1940 - | Great Britain, England ? | 1 | |
| Helen Ostafew | 20th - century | Great Britain, England | 1 |
| Henrique Oswald | 1852 - 1931 | Brazil | 1 |
| José Maria Nemesio Otańo y Eguino | 1880 - 1956 | Spain | 1 |
| Caspar Othmayr | 1515 - 1553 | Germany | 1 |
| Stanislav Otruba | 1868 - 1949 | Czech Republic | 1 | |
| Lorenz Justinian Ott | 1748 - 1805 | Germany | 1 | |
| Matt Ottley | 1962 - | Papua New Guinea | Australia | 1 |
| Ernst Julius Otto | 1804 - 1877 | Germany | 1 |