| Oru & The Yatra, The - Traditional Out-Rigger Water Craft | V. | Vitharana | 1992 | General |
| Our Colony 1880 - Handbook of Victoria, Pictorial & Descriptive | James, Rev | Ballantyne | 1880 | General |
| Our Economic Needs | M.S., Mudaliyar | Karapper | 1940 | General |
| Our George - A Biography of George Edmund De Silva | Jane | Russell | 1981 | Politics |
| Our Heritage - Book 1 (Up To 1500) | G.C. | Mendis | 1969 | History |
| Our Heritage - Book 2 (1500 - 1796) | G.C. | Mendis | 1962 | History |
| Our Heritage - Book 3 (1796 - Second World War) | G.C. | Mendis | 1962 | History |
| Our Lady of Lanka | N/A | N/A | N/A | Religion |
| Our Lady of Lanka | John M | Senaveratna | 1945 | Religion |
| Our Lanka (A Play in Three Acts) | H. Sri | Nissanka | N/A | General |
| Our Legislature | J.R. | Weinman | 1947 | Politics |
| Our Money Grows On Our Trees - Scheme For A National Orchid | Upali | Dias | 1990 | General |
| Our People, Our Potential, Our Pride, Celebrating the 26 Distrcts of Sri Lanka | N/A | N/A | 2014 | General |
| Our Place in the Civilization of the Ancient World | K. | Balasingham | 1918 | General |
| Out of Bondage, A Biography, S. Thondaman | T. | Sabaratnam | 1990 | General |
| Out Of His Life & Thought - F.L.Woodward | D.H. | Panditha Gunewardene | N/A | General |
| Out of the Blue, A Guide to the Marine Mammals of Sri Lanka, Southern India & the Maldives | Howard | Martenstyn | 2013 | General |
| Out Out Brief Candle | M. | Chandrasoma | 1981 | Literature |
| Out Steppes the Don | C.C | de Silva | 1966 | General |
| Out-Door Proctor, The - James Cecil Walter Pereira 1881 | Vijaya | Samaraweera | 2000 | General |
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