| Octet - Collected Plays | Regi | Siriwardena | 1995 | Literature |
| October Revolution - The 50th Anniversary of the | Leslie | Goonewardene | 1967 | Politics |
| October, National Liberation and Ceylon | Pieter | Keuneman | 1967 | Politics |
| Odysey of a Runaway Child, Galle to Australia\'s Goldfields and Beyond | Manouri P. | Senanayake | 2018 | General |
| Odyssey & Living Legacy of Sieur de La Nerolle | Yasmin | Rajapakse | 2018 | History |
| Odyssey inti the Wild | B. A. | Mahipala | 2013 | General |
| Odyssey of the Tooth Relic, The - The Palladium of Sinhalese Royalty | H.S. | De Zylva | 1928 | Religion |
| Of Jasmines and Jamboos | Grace | Mackie | 1993 | General |
| Of Love and Squalor & Other Stories | Mark | Bartholomeusz | 1971 | Literature |
| Of Sri Lanka I Sing - The Life & Times of Devar Surya Sena | N/A | N/A | 1978 | General |
| Of Tamils & Tigers, a Journey through Sri Lanka's War Years | Ben | Bavinck | 2011 | General |
| Of The Father & Of The Son | James J. | Bulner | 1985 | Literature |
| Off Duty - The Ceylon Police Magazine, Vol XV, No 10, February 1941 | N/A | N/A | 1941 | General |
| Offences Under the Penal Code of Ceylon | G.L. | Peiris | 1973 | General |
| Official Ceylon Handbook, The - British Empire Exhibition 1924 | N/A | N/A | 1924 | General |
| Official Language Bill - Parliamentary Debates - Official Report | Government of Sri Lanka | Hansard | 1956 | Politics |
| Olcott's Contribution to the Buddhist Renaissance | Saddamangala, Dr | Karunaratne | 1980 | Religion |
| Old Sinhalese Nursery Rhymes & Songs | Heather | Hamer | 1999 | General |
| Olwyn's Beach Wadiya, Internationally Renowned Sea Food Restaurant | H. M. Mervyn P. | Herath | 2004 | General |
| On A London Times Editorial On The Sri Lankan Problem | QASLU | N/A | 1986 | General |
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