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| Olsen, Tim (1961 - ) U.S.A. |
| Olson, Alejandro (1993 - ) U.S.A. |
| Olsson, Vagn E. (1954 - ) Denmark |
| Omura, Kumiko (1970 - ) Japan |
| Oña, Erik (1961 - ) Argentina |
| Onna, Peter van (1966 - ) The Netherlands |
| Oorebeek, Christina Viola (1944 - ) The Netherlands |
| Oosten, Roel van (1958 - ) The Netherlands |
| Oosterveld, Ernst (1951 - ) The Netherlands |
| Oostrom, Tom van (? - ) U.S.A. |
| Opitz, Bernhard (1967 - ) Germany |
| Oppedisano, Marco (1971 - ) U.S.A. |
| Oppo, Franco (1935 - ) Italy |
| Orbán, György (1947 - ) Hungary |
| Ordway, Scott J. (1984 - ) U.S.A. |
| Ore, Østen Mikal (1967 - ) Denmark |
| Orenstein, Joyce E. (1939 - ) U.S.A. |
| Orff, Carl (1895 - 1982) Germany |
| Orkin, Yevgeni (1977 - ) Ukraine |
| Orozco, Keyla (1969 - ) Cuba |
| Orr, Buxton (1924 - 1997) United Kingdom |
| Orrego-Salas, Juan (1919 - ) Chile |
| Orsi, Andrea (1955 - ) Italy |
| Ortiz, Gabriela (? - ) Mexico |
| Ortiz, Pablo Victor (1956 - ) Argentina |
| Ortiz, Richard (? - ) U.S.A. |
| Ortiz-Alvarado, William (1947 - ) Puerto Rico |
| Ortolan, Edson Tadeu (1958 - ) Brazil |
| Orton, Richard (1940 - ) United Kingdom |
| Orts Ruiz, José Antonio (1955 - ) Spain |
| Ørvad, Timme (1943 - ) Denmark |
| Ory, David (? - ) |
| Osada, Moto (? - ) Japan |
| Osborne, Nigel (1948 - ) United Kingdom |
| Osman, Ali (1958 - ) Sudan |
| Ospald, Klaus (1956 - ) Germany |
| Ostendorf, Jens-Peter (1944 - 2006) Germany |
| Osterfield, Paul (? - ) U.S.A. |
| Österling, Fredrik (1966 - ) Sweden |
| Otero, Francisco (1940 - ) Spain |
| Otondo, Felipe (1972 - ) Chile |
| Ott, Daniel (1960 - ) Switzerland |
| Otte, Erik (? - ) The Netherlands |
| Otte, Hans (1926 - 2007) Germany |
| Ouellette, Antoine (? - ) Canada |
| Ourkouzounov, Atanas (1970 - ) Bulgaria |
| Ovejero, Osvaldo Antonio (1960 - ) Austria |
| Owen, Harold (1931 - ) U.S.A. |
| Owens, Terry Winter (? - ) U.S.A. |
| Ozab, David (1965 - ) U.S.A. |
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