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- Robert C. O'Brien (1918–1973)
- Kevin O'Donnell, Jr. (born 1950)
- Patrick O'Leary (born 1952)
- Vladimir Obruchev (1863–1956)
- Andrew J. Offutt (born 1937)
- Nnedi Okorafor (born 1974)
- Chad Oliver (1928–1993)
- Jerry Oltion (born 1957)
- John Ostrander (born 1949)
- Jerry Ordway (born 1957)
- Marek Oramus (born 1952)
- Rebecca Ore (born 1948)
- George Orwell (1903–1950) (pseudonym of Eric Arthur Blair)
Read more about this topic: List Of Science Fiction Authors