- The Nürnberg StoveAuthor: Ouida, Maria Louise KirkReleased on Project Gutenberg: April 6, 2007
- The O'Conors of Castle Conor, County Mayo: From "Tales from All Countries"Author: Anthony TrollopeReleased on Project Gutenberg: January 1, 2003
- The Oahu College at the Sandwich IslandsAuthor: Punahou SchoolReleased on Project Gutenberg: February 25, 2007
- The Oakdale AffairAuthor: Edgar Rice BurroughsReleased on Project Gutenberg: July 11, 2008
- The Oaths, Signs, Ceremonies and Objects of the Ku-Klux-Klan.: A Full Expose. By A Late MemberAuthor: AnonymousReleased on Project Gutenberg: July 22, 2008
- The Observations of HenryAuthor: Jerome K. (Jerome Klapka) JeromeReleased on Project Gutenberg: March 7, 2006
- The Obstacle RaceAuthor: Ethel M. (Ethel May) DellReleased on Project Gutenberg: March 1, 2004
- The Ocean and Its WondersAuthor: R. M. (Robert Michael) BallantyneReleased on Project Gutenberg: June 7, 2007
- The Ocean Cat's Paw: The Story of a Strange CruiseAuthor: George Manville Fenn, W. S. (Walter S.) StaceyReleased on Project Gutenberg: May 8, 2007
- The Octopus : A Story of CaliforniaAuthor: Frank NorrisReleased on Project Gutenberg: July 11, 2008
- The Odd WomenAuthor: George GissingReleased on Project Gutenberg: August 1, 2003
- The Odds: And Other StoriesAuthor: Ethel M. (Ethel May) DellReleased on Project Gutenberg: July 28, 2005
- The Odes and Carmen Saeculare of HoraceAuthor: Horace, 66 BCE-9 BCE, John ConingtonReleased on Project Gutenberg: April 1, 2004
- The Odes of Casimire, Translated by G. HilsAuthor: Maciej Kazimierz Sarbiewski, Roestvig, Maren-Sofie [Commentator], Hils, G. [Translator]Released on Project Gutenberg: April 12, 2008
- The OdysseyAuthor: Homer, Alexander PopeReleased on Project Gutenberg: April 1, 2002
- The Odyssey: Rendered into English prose for the use of those who cannot read the originalAuthor: Homer, Samuel ButlerReleased on Project Gutenberg: April 1, 1999
- The Odyssey of HomerAuthor: Homer, S. H. (Samuel Henry) Butcher, Andrew LangReleased on Project Gutenberg: April 1, 1999
- The Odyssey of HomerAuthor: Homer, William CowperReleased on Project Gutenberg: January 13, 2008
- The Old Apple Dealer (From "Mosses from an Old Manse")Author: Nathaniel HawthorneReleased on Project Gutenberg: November 1, 2005
- The Old Bachelor: A ComedyAuthor: William Congreve, G. S. (George Slythe) StreetReleased on Project Gutenberg: February 1, 1998
- The Old Bell of Independence; Or, Philadelphia in 1776Author: Henry C. (Henry Clay) WatsonReleased on Project Gutenberg: March 1, 2004
- The Old Bush SongsAuthor: A. B. (Andrew Barton) PatersonReleased on Project Gutenberg: December 1, 2003
- The Old Castle and Other StoriesAuthor: AnonymousReleased on Project Gutenberg: May 2, 2007
- The Old Coast Road: From Boston to PlymouthAuthor: Agnes RotheryReleased on Project Gutenberg: June 21, 2007
- The Old Curiosity ShopAuthor: Charles DickensReleased on Project Gutenberg: October 1, 1996
- The Old English Baron: a Gothic StoryAuthor: Clara ReeveReleased on Project Gutenberg: February 1, 2004
- The Old English PhysiologusAuthor: Albert S. (Albert Stanburrough) Cook, Cynewulf, James Hall PitmanReleased on Project Gutenberg: December 30, 2004
- The Old Flute-Player: A Romance of To-dayAuthor: Edward Marshall, Charles Turner Dazey, Hare, J. Knowles [Illustrator], Clarence RoweReleased on Project Gutenberg: February 23, 2006
- The Old Folks' Party: 1898Author: Edward BellamyReleased on Project Gutenberg: September 21, 2007
- The Old Franciscan Missions Of CaliforniaAuthor: George Wharton JamesReleased on Project Gutenberg: October 25, 2004
- The Old Front LineAuthor: John MasefieldReleased on Project Gutenberg: February 18, 2007
- The Old Gray HomesteadAuthor: Frances Parkinson KeyesReleased on Project Gutenberg: January 1, 2006
- The Old HomesteadAuthor: Ann S. (Ann Sophia) StephensReleased on Project Gutenberg: May 1, 2005
- The Old Man in the CornerAuthor: Orczy, Emmuska Orczy, BaronessReleased on Project Gutenberg: January 1, 2004
- The Old Man of the Sea: Ship's Company, Part 11.Author: W. W. (William Wymark) Jacobs, Will OwenReleased on Project Gutenberg: January 1, 2004
- The old man's bagAuthor: T. W. H. (Thomas William Hodgson) Crosland, Monsell, J. R. [Illustrator]Released on Project Gutenberg: November 15, 2007
- The Old Manse (From "Mosses from an Old Manse")Author: Nathaniel HawthorneReleased on Project Gutenberg: November 1, 2005
- The Old Masters and Their Pictures, For the Use of Schools and Learners in ArtAuthor: Sarah TytlerReleased on Project Gutenberg: November 19, 2006
- The Old Merchant Marine: A Chronicle of American Ships and SailorsAuthor: Ralph Delahaye PaineReleased on Project Gutenberg: February 1, 2002
- The Old Northwest: A Chronicle of the Ohio Valley and BeyondAuthor: Frederic Austin Ogg, Allen JohnsonReleased on Project Gutenberg: January 1, 2002
- The Old Peabody Pew: A Christmas Romance of a Country ChurchAuthor: Kate Douglas Smith WigginReleased on Project Gutenberg: September 1, 1999
- The Old Roman World : the Grandeur and Failure of Its Civilization.Author: John LordReleased on Project Gutenberg: November 1, 2004
- The Old Santa Fe Trail: The Story of a Great HighwayAuthor: Henry Inman, Buffalo BillReleased on Project Gutenberg: April 1, 2005
- The Old Stone HouseAuthor: Constance Fenimore WoolsonReleased on Project Gutenberg: October 1, 2004
- The Old Stone House and Other StoriesAuthor: Anna Katharine GreenReleased on Project Gutenberg: June 13, 2007
- The Old Wives' TaleAuthor: Arnold BennettReleased on Project Gutenberg: March 1, 2004
- The Olden Time Series, Vol. 1: Curiosities of the Old Lottery: Gleanings Chiefly from Old Newspapers of Boston and Salem, MassachusettsAuthor: Henry M. (Henry Mason) BrooksReleased on Project Gutenberg: March 12, 2006
- The Olden Time Series, Vol. 3: New-England Sunday: Gleanings Chiefly From Old Newspapers Of Boston And Salem, MassachusettsAuthor: Henry M. (Henry Mason) BrooksReleased on Project Gutenberg: January 9, 2006
- The Olden Time Series, Vol. 4: Quaint and Curious Advertisements: Gleanings Chiefly from Old Newspapers of Boston and Salem, MassachusettsAuthor: Henry M. (Henry Mason) BrooksReleased on Project Gutenberg: June 4, 2007
- The Olden Time Series, Vol. 5: Some Strange and Curious Punishments: Gleanings Chiefly from Old Newspapers of Boston and Salem, MassachusettsAuthor: Henry M. (Henry Mason) BrooksReleased on Project Gutenberg: August 3, 2005
- The Olden Time Series, Vol. 6: Literary Curiosities: Gleanings Chiefly from Old Newspapers of Boston and Salem, MassachusettsAuthor: Henry M. (Henry Mason) BrooksReleased on Project Gutenberg: June 26, 2006
- The Olden Time Series: Vol. 2: The Days of the Spinning-Wheel in New England: Gleanings Chiefly from old Newspapers of Boston and Salem, MassachusettsAuthor: Henry M. (Henry Mason) BrooksReleased on Project Gutenberg: August 26, 2007
- The Oldest Code of Laws in the World: The code of laws promulgated by Hammurabi, King of Babylon, B.C. 2285-2242Author: Hammurabi, King of Babylonia, C. H. W. (Claude Hermann Walter) JohnsReleased on Project Gutenberg: November 25, 2005
- The Olynthiacs and the Phillippics of Demosthenes: Literally translated with notesAuthor: Demosthenes, Charles Rann KennedyReleased on Project Gutenberg: November 1, 2004
- The one great realityAuthor: Louisa Clayton, Evan Henry HopkinsReleased on Project Gutenberg: March 1, 2005
- The One Moss-RoseAuthor: Philip Bennett PowerReleased on Project Gutenberg: April 26, 2007
- The One Woman: A Story of Modern UtopiaAuthor: Dixon, Thomas, Jr.Released on Project Gutenberg: July 1, 2004
- The Online WorldAuthor: Odd De PresnoReleased on Project Gutenberg: September 1, 1993
- The Onlooker, Volume 1, Part 2Author: Various, Alfred Henry LewisReleased on Project Gutenberg: September 11, 2005
- The Only True Mother Goose MelodiesAuthor: AnonymousReleased on Project Gutenberg: January 1, 2004