| Author | Titles | | 1.
| Onuorah, Mitchell | 1 | | 2.
| O&O Baukunst (Firma de Arquitectura) | 1 | | 3.
| Oo, Peter Sein Hlaing | 1 | | 4.
| Oom, Frederico, 1899- | 7 | | 5.
| Oom, João, 1938- | 7 | | 6.
| Oom, Maria Manuela de Campos, 1909-2008 | 1 | | 7.
| Oom, Pedro, 1926-1974 | 9 | | 8.
| Oom, Rosa | 1 | | 9.
| Oorebeek, Willem, 1953- | 2 | | 10.
| Oort, Jan van, activ. 1645-1699 | 1 |
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