- Olsen, Bob; pseudonym of Alfred J. Olsen, Jr. (1884-1956) (stories) (assoc.)
- See www.sf-encyclopedia.com/entry/olsen_bob
- Olsen, Gregg (Donald) (1959- ) (stories) (assoc.)
- See en.wikipedia.org/wiki/Gregg_Olsen
- Olsen, Jack [i.e., John Edward Olsen] (1925-2002) (stories)
- Journalist, correspondent for Time magazine, editor of Sports Illustrated magazine; living in Washington state.
- Olsen, Jon S. (fl. 2000s-2010s) (stories)
- See www.waste.org/burnunit
- Olsen, Sondra Spatt (1936-2013) (stories)
- See specialcollections.vassar.edu/collections/manuscripts/findingaids/olsen_sondra.html
- Olson, Amanda M. (fl. 2010s) (stories)
- See www.beneath-ceaseless-skies.com/authors/amanda-m-olson/
- Olson, Cliff(ord Oren) (1905-?) (stories)
- See en.wikipedia.org/wiki/Cliff_Olson
- Olson, Danel (1965- ) (stories)
- See www.centipedepress.com/authors/olson.html
- Olson, Eugene E. (1936-2018) (stories)
- See en.wikipedia.org/wiki/Brad_Steiger
- Olson, Maribeth (fl. 1950s-1960s) (art)
- See todaysinspiration.blogspot.co.uk/2013/06/the-art-of-wow-featuring-maribeth-olson.html
- Olson, Melissa F. (fl. 2010s) (stories) (assoc.)
- See melissafolson.com
- Olsson, Fredrik T. (1969- ) (stories) (assoc.)
- See fredriktolsson.se
- Oltuski, Alicia (fl. 2010s) (stories)
- See aliciaoltuski.com
- Olver, Stuart (fl. 2010s) (stories)
- See midnightechomagazine.com/2015/04/14/meet-the-writer-stuart-olver
- OMahony, Charles Kingston (1884-1944) (stories)
- Born in Mitchelstown, County Cork, Ireland; educated in Dublin; author and journalist.
- OMalley, Kathleen (Ann) (1955- ) (stories) (assoc.)
- See www.sf-encyclopedia.com/entry/omalley_kathleen
- OMalley, Power [born Michael Augustine Power] (1877-1946) (art)
- See en.wikipedia.org/wiki/Power_OMalley
- Oman, Carola [i.e., Carola Mary Anima Oman Lenanton] (1897-1978) (stories)
- See en.wikipedia.org/wiki/Carola_Oman
- Oman, [Sir] Charles (William Chadwick) (1860-1946) (stories)
- See en.wikipedia.org/wiki/Charles_Oman
- OMeara, Kathleen (1839-1888) (stories)
- Born in Dublin, grew up in France; traveled widely; for many years Paris correspondent of The Tablet, a Catholic journal; died in Paris.
- OMeara, Mallory (fl. 2010s) (stories)
- See www.malloryomeara.com
- Omessa, Charles (1883-1933) (stories)
- See data.bnf.fr/13306603/charles_omessa
- ONeail, N(orbert) J(ames) (1898-1972) (stories)
- See tellersofweirdtales.blogspot.com/2012/03/nj-oneail-1898-1972.html
- ONeal, Patrick (Wisdom) (1927-1994) (stories) (assoc.)
- See en.wikipedia.org/wiki/Patrick_O%27Neal_(actor)
- ONeil, Denny [i.e., Dennis Joseph ONeil] (1939- ) (stories)
- See www.sf-encyclopedia.com/entry/oneil_dennis
- ONeill, Charles Kendall (1909-1997) (stories)
- See www.nytimes.com/1997/06/30/arts/charles-o-neill-87-tv-and-history-writer.html
- ONeill, Gerard K(itchen) (1927-1992) (stories) (assoc.)
- See en.wikipedia.org/wiki/Gerard_K._O%27Neill
- ONeill, John (fl. 2000s-2010s) (stories)
- See en.wikipedia.org/wiki/John_O%27Neill_(editor)
- ONeill, Joseph (James) (1878-1952) (stories) (assoc.)
- See www.sf-encyclopedia.com/entry/oneill_joseph
- ONeill, Joseph (1964- ) (stories)
- See en.wikipedia.org/wiki/Joseph_O%27Neill_(writer)
- ONeill, Kevin (1953- ) (stories) (art) (assoc.)
- See en.wikipedia.org/wiki/Kevin_O%27Neill_(comics)
- ONeill, Peggy [i.e., Margaret ONeill Eaton] (1799-1879) (stories) (assoc.)
- See en.wikipedia.org/wiki/Margaret_O%27Neill_Eaton
- ONeill, Rose Cecil [Mrs. Harry Leon Wilson] (1874-1944) (stories) (art)
- Born in Wilkesbarre, Pennsylvania.
- Ong, Han (1968- ) (stories)
- See en.wikipedia.org/wiki/Han_Ong
- Onions, (George) Oliver (1873-1961) (stories) (art) (assoc.)
- Changed his name legally to George Oliver in 1918, but continued to write as Oliver Onions.
- Onopa, Robert (1943- ) (stories) (assoc.)
- See www.sf-encyclopedia.com/entry/onopa_robert
- Onslow, Augusta Geraldine ({c}1865-1960) (stories)
- See www.thepeerage.com/p54676.htm
- Onslow, Florence Coulston [née Gardener] (1853-1934) (stories)
- See www.wikitree.com/wiki/Gardener-126
- Onslow, John (1906-1985) (stories)
- See bearalley.blogspot.co.uk/2015/04/john-onslow.html
- Onspaugh, Mark (fl. 1980s-2010s) (stories)
- See www.markonspaugh.com
- Onwualu, Chinelo (fl. 2010s) (stories)
- See chineloonwualu.blogspot.co.uk
- Onyebuchi, Tochi (fl. 2000s-2010s) (stories)
- See treize64.livejournal.com
- Oparin, Aleksandr Ivanovich (1894-1980) (stories) (assoc.)
- See en.wikipedia.org/wiki/Alexander_Oparin
- Opatoshu, Joseph [born Josef Mair Opatowski] (1886-1954) (stories)
- See culture.pl/en/artist/joseph-opatoshu-josef-meir-opatowski
- Openshaw, George H(arry) (1882-?) (stories)
- Birth in Birmingham, England, registered as George Henry Openshaw; probably died in Kenya, to which he sailed in 1946, apparently intending to live there.
- Opie, Peter (1918-1982) (stories)
- See en.wikipedia.org/wiki/Iona_and_Peter_Opie
- Öpik, Ernst J(ulius) (1893-1985) (stories) (assoc.)
- See en.wikipedia.org/wiki/Ernst_%C3%96pik
- Oppenheim, E(dward) Phillips (1866-1946) (stories) (assoc.)
- See www.sf-encyclopedia.com/entry/oppenheim_e_phillips
- Oppenheimer, J(ulius) Robert (1904-1967) (stories) (assoc.)
- See en.wikipedia.org/wiki/J._Robert_Oppenheimer
- Oppenheimer, Joshua (1974- ) (stories) (assoc.)
- See en.wikipedia.org/wiki/Joshua_Oppenheimer
- Opperman, K. A. (fl. 2010s) (stories) (assoc.)
- See kaopperman1.blogspot.co.uk
- Opperman, Meg (fl. 2010s) (stories)
- See megopperman.com
- Orage, Alfred R(ichard) (1873-1934) (stories) (assoc.)
- See en.wikipedia.org/wiki/Alfred_Richard_Orage
- Oram, Jo (fl. 2010s) (stories)
- See joiswriting.wordpress.com
- Orban, Paul (1896-1974) (stories) (art) (assoc.)
- See pulpartists.com/Orban.html
- Orbitowski, Łukasz (1977- ) (stories)
- See en.wikipedia.org/wiki/%C5%81ukasz_Orbitowski
- Orchardson, [Sir] William Quiller (1832-1910) (stories) (art) (assoc.)
- See en.wikipedia.org/wiki/William_Quiller_Orchardson
- Orcutt, Eddy (fl. 1930s-1950s) (stories)
- Almost certainly resident in San Diego, California.
- Orcutt, William Dana (1870-1953) (stories)
- Born in Lebanon, New Hampshire; died in Boston; Harvard graduate, typographer and author.
- Orczy, Baroness (Emmuska) [i.e., Emma Magdalena Rosalia Maria Josefa Barbara Barstow, Baroness Orczy] (1865-1947) (stories) (assoc.)
- See en.wikipedia.org/wiki/Baroness_Emma_Orczy
- Orde-Lees, [Major] Thomas (Hans) (1877-1958) (stories) (assoc.)
- See en.wikipedia.org/wiki/Thomas_Orde-Lees
- Ordish, Thomas Fairman (1855-1924) (stories)
- See www.folkplay.info/Ordish/Biography.htm
- Ordoñez, Justin (fl. 2010s) (stories)
- See www.sykosa.com/bio.html
- Ordoñez, Raphael (fl. 2010s) (stories)
- See raphordo.blogspot.co.uk
- Ordover, John J. (1962- ) (stories) (assoc.)
- See en.wikipedia.org/wiki/John_J._Ordover
- Ordway, Frederick I., III (1927-2014) (stories)
- See en.wikipedia.org/wiki/Frederick_I._Ordway_III
- Ordway, (Lucius) Peter (1916-2001) (stories)
- Born in Minnesota; died in Palm Beach, Florida; scriptwriter and novelist.
- Ore, Rebecca; pseudonym of Rebecca Brown (1948- ) (stories) (assoc.)
- See www.sf-encyclopedia.com/entry/ore_rebecca
- OReilly, Dowell (Philip) (1865-1923) (stories)
- See en.wikipedia.org/wiki/Dowell_Philip_O%27Reilly
- OReilly, Edward S(innott) Tex (1880-1946) (stories)
- Writer and journalist.
- OReilly, Finbarr (fl. 2010s) (stories)
- See finoreilly.wordpress.com
- OReilly, Jane (fl. 2010s) (stories) (assoc.)
- See www.janeoreilly.co.uk
- OReilly, John (1907- ) (stories)
- See www.sf-encyclopedia.com/entry/oreilly_john
- OReilly, John Boyle (1844-1890) (stories)
- See www.sf-encyclopedia.com/entry/oreilly_john_boyle
- OReilly, Mary Boyle (1873-1937) (stories)
- Born in Boston.
- OReilly, Nero (fl. 2010s) (stories)
- See www.trumpetshark.com
- Orejudos, Domingo (Stephen) (fl. 1930s-1990s) (art)
- See gayinfluence.blogspot.co.uk/2011/09/etienne-aka-domingo-stephan-orejudos.html
- Oreskes, Naomi (1958- ) (stories) (assoc.)
- See en.wikipedia.org/wiki/Naomi_Oreskes
- Oreto, Frank (fl. 2010s) (stories)
- See fantasyscrollmag.com/authors/frank-oreto/
- Orgill, Douglas (William) (1922-1984) (stories) (assoc.)
- See www.sf-encyclopedia.com/entry/orgill_douglas
- Orhan, Kenan (fl. 2010s) (stories)
- See newfoundjournal.org/archives/volume-6/issue-3/fiction-kenan-orhan
- ORiordan, Conal Holmes OConnell (1874-1948) (stories)
- See en.wikipedia.org/wiki/Conal_Holmes_O%27Connell_O%27Riordan
- Orloff, Alan (fl. 2010s) (stories) (assoc.)
- See www.alanorloff.com/alan.html
- Orman, Kate (1968- ) (stories) (assoc.)
- See www.sf-encyclopedia.com/entry/orman_kate
- Ormant, Arthur (1922- ) (stories)
- Editor and writer. Born in Albany, New York; lives in New York City.
- Ormerod, John (1927- ) (stories)
- See Born in Lancashire; served in the Merchant Navy from 1943-47; worked as a newspaper reporter for a year and then abandoned office life to concentrate on writing.
- Ormes, Nene (1975- ) (stories)
- See sv.wikipedia.org/wiki/Nene_Ormes
- Ormsbee, Agnes Bailey (1858-1920) (stories)
- See findagrave.com/cgi-bin/fg.cgi/http=://www,findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=62896328
- Ormsby, Frank [i.e., Francis Arthur Ormsby] (1947- ) (stories)
- See en.wikipedia.org/wiki/Frank_Ormsby
- Ormsby, Stephen C. (fl. 2010s) (stories)
- See stephenormsby.wordpress.com
- Orne, Caroline (née Chaplin) (?-1882) (stories)
- See en.wikisource.org/wiki/The_Female_Prose_Writers_of_America:_With_Portraits,_Biographical_Notices,_and_Specimens_of_their_Writings/Caroline_Orne
- Orne, Caroline F(rances) (1818-1905) (stories)
- See www2.cambridgema.gov/Historic/CWHP/bios_o.html
- Oronhyatekha, Dr. (1841-1907) (stories) (assoc.)
- See en.wikipedia.org/wiki/Oronhyatekha
- ORourke, Frank (1916-1989) (stories) (assoc.)
- See www.sf-encyclopedia.com/entry/orourke_frank
- ORourke, Joe [i.e., Joseph Leo ORourke, Jr.] (1904-1990) (stories)
- See en.wikipedia.org/wiki/Joe_O%27Rourke
- ORourke, (Francis) Michael (1941-2001) (stories)
- A Lawyer in Minnesota.
- ORourke, Monica J. (fl. 1990s-2010s) (stories)
- See www.smashwords.com/profile/view/MonicaORourke