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- Odd John by Olaf Stapledon
- Oh. My. Gods. by Tera Lynn Childs
- Old Man's War by John Scalzi
- Omega by Jack McDevitt
- On the Beach by Nevil Shute
- On Wings of Song by Thomas M. Disch
- One in Three Hundred by J. T. McIntosh
- One Million Tomorrows by Bob Shaw
- One Mind's Eye by Kathy Tyers
- Operation Columbus by Hugh Walters
- The Ophiuchi Hotline by John Varley
- Optiman by Brian Stableford
- Oryx and Crake by Margaret Atwood.
- Otherland series by Tad Williams
- namely, City of Golden Shadow, River of Blue Fire, Mountain of Black Glass, and Sea of Silver Light
- Out of the Deeps (aka The Kraken Wakes) by John Wyndham
- The Outlaws of Mars by Otis Adelbert Kline
Read more about this topic: List Of Science Fiction Novels