| Ó Riada, Seán (1931 - 1971) Ireland |
| O'Brien, Benjamin (? - ) U.S.A. |
| O'Brien, JoyEllen (? - ) U.S.A. |
| O'Connell, Katharine (1971 - ) U.S.A. |
| O'Connell, Kevin (1958 - ) Ireland |
| O'Connor, Neil (1979 - ) Ireland |
| O'Doherty, Brian (? - ) |
| O'Dwyer, Timothy (1971 - ) Australia |
| O'Leary, Jane (1946 - ) Ireland |
| O'Leary, Martin (1963 - ) Ireland |
| O'Neill, Nicholas (1970 - ) United Kingdom |
| O'Regan, Tarik (1978 - ) United Kingdom |
| O'Riordan, Kirk (1968 - ) U.S.A. |
| Obermaier, Klaus (1955 - ) Austria |
| Obermayer, Klaus (1943 - ) Germany |
| Obermüller, Karola (1977 - ) Germany |
| Obieglo, Lorenz (? - ) |
| Obrovská, Jana (1930 - 1987) Czech Republic |
| Ocampo, Sergio (? - ) Mexico |
| Ocaña, Anthony (1980 - ) Spain |
| Ochi, Takashi (1934 - 2010) Japan |
| Ochoa, Luis (1959 - ) Venezuela |
| Ochs, Gerd (1903 - 1977) Germany |
| Ockenfels, Helmut (1937 - 1999) Germany |
| Ockert, Matthias (1970 - ) Germany |
| Odaira, Koichi (1960 - ) Japan |
| Odriozola, Ricardo (1965 - ) Norway |
| Odstrcil, Karel (1930 - 1997) Czech Republic |
| Oehring, Helmut (1961 - ) Germany |
| Oesterle, Michael (1968 - ) Canada |
