 | Donal O'Danachair, | The Poetical Works of John Milton |
 | Kakuzo Okakura | The Book of Tea |
 | Charles Oliver | ABC's of Science |
 | E. Phillips Oppenheim | The Malefactor |
 | E. Phillips Oppenheim | The Yellow Crayon, E. Phillips Oppenheim |
 | Oppenheim | The Kingdom of the Blind |
 | Oppenheim | The Vanished Messenger |
 | Oppenheim | A Millionaire of Yesterday |
 | Oppenheim | The Illustrious Prince |
 | Oppenheim | The Zeppelin's Passenger |
 | Oliver Optic | Poor and Proud |
 | Baroness Orczy | The Scarlet Pimpernel |
 | Baroness Orczy | El Dorado |
 | Mrs. Sutherland Orr | Orr's Life/Letters of Robert Browning |
 | Stevenson & Osbourne | The Wrong Box |
 | Stevenson & Osbourne | The Wrong Box |
 | Stevenson & Osbourne | The Ebb-Tide |
 | William Osler | The Evolution of Modern Medicine |
 | Wilfred Owen | Poems |