| Author | Titles | | 1.
| Orozco, Gabriel, 1962- | 15 | | 2.
| Orozco, José Clemente, 1883-1949 | 1 | | 3.
| Orpheus Gallery (Belfast) | 1 | | 4.
| Orr, Boyd | 1 | | 5.
| Orr, Chris, 1943- | 2 | | 6.
| Orr, Christopher, 1943- | 0 | | 7.
| Author is: Orr, Chris, 1943- | 2 | | 8.
| Orr, Christopher John, 1943- | 0 | | 9.
| Author is: Orr, Chris, 1943- | 2 | | 10.
| Orr, Emily | 1 | | 11.
| Orr, John | 1 | | 12.
| Orr, John Boyd, 1880-1971 | 1 |
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