- Ohnaka, Kathryn (fl. 2010s) (stories)
- See www.kathrynohnaka.com
- OKeefe, Claudia (Diane) (1958- ) (stories) (assoc.)
- See www.sf-encyclopedia.com/entry/okeefe_claudia
- OKeefe, Megan E. (fl. 2010s) (stories)
- See meganokeefe.com
- OKeefe, Rose (fl. 2010s) (stories)
- See litreactor.com/team/rose-okeefe
- Okorafor, Nnedi(mma Nkemdili) (1974- ) (stories) (assoc.)
- See en.wikipedia.org/wiki/Nnedi_Okorafor
- Okungbowa, Suyi Davies (fl. 2010s) (stories)
- See suyidavies.com
- Olander, Joseph D(avid) (1939- ) (stories) (assoc.)
- See www.sf-encyclopedia.com/entry/olander_joseph_d
- Old Scout, An; house pseudonym (fl. 1910s-1920s) (stories)
- See www.sf-encyclopedia.com/entry/old_scout_an
- Olde Heuvelt, Thomas (1983- ) (stories)
- See en.wikipedia.org/wiki/Thomas_Olde_Heuvelt
- Older, Daniel José (1980- ) (stories)
- See ghoststar.net
- Older, Malka (fl. 2010s) (stories)
- See us.macmillan.com/author/malkaolder
- Oldfield, Claude Houghton (1889-1961) (stories)
- Born in Sevenoaks, Kent, England; chartered accountant, civil servant and writer.
- Oldknow, Antony (fl. 1990s-2010s) (stories)
- See www.enmu.edu/about/mmemo/2012/april%202
- OLeary, Brian (Todd) (1940- ) (stories)
- See www.sf-encyclopedia.com/entry/oleary_brian
- OLeary, P(atrick) R. (fl. 2010s) (stories)
- See proleary.com
- OLeary, Patrick (1952- ) (stories) (assoc.)
- See www.sf-encyclopedia.com/entry/oleary_patrick
- Oleastri, Luca (fl. 2010s) (art)
- See www.innovari.it
- Olejniczak, Patryk (fl. 2010s) (art)
- See patryk-garrett.deviantart.com
- Oliva, Alexandra (fl. 2010s) (stories) (assoc.)
- See www.alexandraoliva.com
- Oliver, Anton M(aracek) (1888-1977?) (stories)
- See tellersofweirdtales.blogspot.co.uk/2013/12/anton-m-oliver-1888-1977.html
- Oliver, (Symmes) Chad(wick) (1928-1993) (stories) (assoc.)
- See www.sf-encyclopedia.com/entry/oliver_chad
- Oliver, Jonathan (fl. 2000s-2010s) (stories)
- See jonoliverwriter.blogspot.co.uk
- Oliver, Lauren (fl. 2010s) (stories) (assoc.)
- See www.sf-encyclopedia.com/entry/oliver_lauren
- Olivieri, Irene Hardwicke (fl. 2000s-2010s) (art)
- See www.irenehardwickeolivieri.com
- Olmsted, Harry F(rancis) (1889-1970) (stories)
- Born August 10, 1889 in Los Angeles; worked as a civil engineer before turning to fiction; claimed to have sold 1200 stories; died April 2, 1970 in Riverside, California.
- Olsen, Bob; pseudonym of Alfred J. Olsen, Jr. (1884-1956) (stories) (assoc.)
- See www.sf-encyclopedia.com/entry/olsen_bob
- Olsen, Jon S. (fl. 2000s-2010s) (stories)
- See www.waste.org/burnunit
- Olson, Amanda M. (fl. 2010s) (stories)
- See www.beneath-ceaseless-skies.com/authors/amanda-m-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, Melissa F. (fl. 2010s) (stories) (assoc.)
- See melissafolson.com
- Olsson, Fredrik T. (1969- ) (stories) (assoc.)
- See fredriktolsson.se
- Olver, Stuart (fl. 2010s) (stories)
- See midnightechomagazine.com/2015/04/14/meet-the-writer-stuart-olver
- OMalley, Kathleen (Ann) (1955- ) (stories) (assoc.)
- See www.sf-encyclopedia.com/entry/omalley_kathleen
- OMeara, Mallory (fl. 2010s) (stories)
- See www.malloryomeara.com
- ONeail, N(orbert) J(ames) (1898-1972) (stories)
- See tellersofweirdtales.blogspot.com/2012/03/nj-oneail-1898-1972.html
- ONeil, Denny [i.e., Dennis Joseph ONeil] (1939- ) (stories)
- See www.sf-encyclopedia.com/entry/oneil_dennis
- 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, Kevin (1953- ) (stories) (art) (assoc.)
- See en.wikipedia.org/wiki/Kevin_O%27Neill_(comics)
- Onions, (George) Oliver (1873-1961) (stories) (assoc.)
- Changed his name legally to George Oliver in 1918, but continued to write as Oliver Onions.
- Onopa, Robert (1943- ) (stories)
- See www.sf-encyclopedia.com/entry/onopa_robert
- 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
- 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.
- 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, Joshua (1974- ) (stories) (assoc.)
- See en.wikipedia.org/wiki/Joshua_Oppenheimer
- Opperman, K. A. (fl. 2010s) (stories) (assoc.)
- See kaopperman1.blogspot.co.uk
- Oram, Jo (fl. 2010s) (stories)
- See joiswriting.wordpress.com
- Orban, Paul (1896-1974) (art)
- See pulpartists.com/Orban.html
- Orbitowski, Łukasz (1977- ) (stories)
- See en.wikipedia.org/wiki/%C5%81ukasz_Orbitowski
- 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
- Ore, Rebecca; pseudonym of Rebecca Brown (1948- ) (stories) (assoc.)
- See www.sf-encyclopedia.com/entry/ore_rebecca
- OReilly, Finbarr (fl. 2010s) (stories)
- See finoreilly.wordpress.com
- OReilly, Jane (fl. 2010s) (stories) (assoc.)
- See www.janeoreilly.co.uk
- 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
- Orman, Kate (1968- ) (stories) (assoc.)
- See www.sf-encyclopedia.com/entry/orman_kate
- Ormes, Nene (1975- ) (stories)
- See sv.wikipedia.org/wiki/Nene_Ormes
- Ormsby, Stephen C. (fl. 2010s) (stories)
- See stephenormsby.wordpress.com
- ORourke, (Francis) Michael (1941-2001) (stories)
- A Lawyer in Minnesota.
- ORourke, Monica J. (fl. 1990s-2010s) (stories)
- See www.smashwords.com/profile/view/MonicaORourke
- Ortega, Francisco (1974- ) (stories)
- See en.wikipedia.org/wiki/Francisco_Ortega_(writer)
- Ortiz, Karla ({c}1985- ) (art)
- See karlaortizart.blogspot.co.uk
- Ortlieb, Marc (fl. 1970s-1990s) (stories) (assoc.)
- See fancyclopedia.org/marc-ortlieb
- Orullian, Peter (1969- ) (stories) (assoc.)
- See en.wikipedia.org/wiki/Peter_Orullian
- Orwell, George; pseudonym of Eric Blair (1903-1950) (stories) (assoc.)
- See en.wikipedia.org/wiki/George_Orwell
- Osborn, Marijane (fl. 1980s-2010s) (stories)
- See english.ucdavis.edu/people/directory/ansuz
- Osborne, Cary G. (fl. 1980s-2010s) (stories)
- See iroshioftheglaive.blogspot.co.uk
- Osborne, Emily (fl. 2010s) (art)
- See emko.carbonmade.com
- Osborne, Emma (K.) (fl. 2010s) (stories) (assoc.)
- See emmakosborne.com
- Osborne, J. David (fl. 2010s) (stories)
- See www.brokenriverbooks.com
- Osborne, Stephanie (fl. 2010s) (stories)
- See www.sff.net/people/steph-osborn
- Osborne, William Hamilton (1873-1942) (stories)
- See www.jerseyhistory.org/findingaid.php?aid=1137
- Osgood, Irene ({c}1869-1922) (stories)
- Born Irene De Belot near Richmond, Virginia; married someone named Osgood, then Charles Piggot Harvey, then Robert Sherard.
- Osgood, Kate Putnam (1841-1910) (stories)
- See en.wikisource.org/wiki/Author:Kate_Putnam_Osgood
- OShaughnessy, Arthur W(illiam Edgar) (1844-1881) (stories)
- See en.wikipedia.org/wiki/Arthur_O%27Shaughnessy
- Oshiro, Mark (fl. 2010s) (stories)
- See markdoesstuff.tumblr.com
- Osias, Kate (Aton) (fl. 2000s-2010s) (stories)
- See wishcatcher.blogspot.co.uk
- Ostow, Micol (1976- ) (stories)
- See en.wikipedia.org/wiki/Micol_Ostow
- Ostrovski, Emil (fl. 2010s) (stories)
- See www.emilostrovski.com
- Ostrovsky, Andrew (fl. 2010s) (art)
- See agsandrew.deviantart.com
- OSullivan, Patrick (fl. 2010s) (stories)
- See patrickcosullivan.com
- OSullivan, Vincent (1868-1940) (stories)
- See modjourn.org/render.php?view=mjp_object&id=mjp.2005.01.028
- OSullivan, William (fl. 1900s-1960s) (stories)
- probably a house pseudonym.
- Otis, Abbey Mei (fl. 2010s) (stories)
- See www.goodreads.com/author/show/5456552.Abbey_Mei_Otis
- OToole, George J. (1936-2001) (stories)
- See www.sf-encyclopedia.com/entry/otoole_george
- Ott, Anthony B. (fl. 1940s-1950s) (stories)
- possibly a pseudonym.
- Ott, [Dr.] John N(ash) (1909-2000) (stories) (assoc.)
- See en.wikipedia.org/wiki/John_Ott
- Ottaviani, Jim (1963- ) (stories)
- See en.wikipedia.org/wiki/Jim_Ottaviani
- Otus, Erol (fl. 1970s-2010s) (stories) (assoc.)
- See en.wikipedia.org/wiki/Erol_Otus
- Ouellette, Pierre (1945- ) (stories) (assoc.)
- See www.sf-encyclopedia.com/entry/ouellette_pierre