- Our Pirate Hoard: 1891Author: Thomas A. (Thomas Allibone) JanvierReleased on Project Gutenberg: December 10, 2007
- Our Profession and Other PoemsAuthor: Jared BarhiteReleased on Project Gutenberg: October 2, 2006
- Our Sailors: Gallant Deeds of the British Navy during Victoria's ReignAuthor: William Henry Giles KingstonReleased on Project Gutenberg: May 9, 2007
- Our SaviourAuthor: AnonymousReleased on Project Gutenberg: February 1, 2004
- Our Soldier BoyAuthor: George Manville Fenn, Venner, Victor [Illustrator]Released on Project Gutenberg: May 8, 2007
- Our Soldiers: Gallant Deeds of the British Army during Victoria's ReignAuthor: William Henry Giles KingstonReleased on Project Gutenberg: October 17, 2007
- Our Stage and Its Critics: By "E.F.S." of "The Westminster Gazette"Author: Edward Fordham SpenceReleased on Project Gutenberg: September 9, 2004
- Our Unitarian GospelAuthor: Minot J. (Minot Judson) SavageReleased on Project Gutenberg: June 13, 2006
- Our Vanishing Wild Life: Its Extermination and PreservationAuthor: William T. (William Temple) HornadayReleased on Project Gutenberg: August 22, 2004
- Our VillageAuthor: Mary Russell MitfordReleased on Project Gutenberg: February 1, 2001
- Our War with Spain for Cuba's FreedomAuthor: Trumbull WhiteReleased on Project Gutenberg: July 1, 2003
- Our World; Or, the Slaveholder's DaughterAuthor: F. Colburn (Francis Colburn) AdamsReleased on Project Gutenberg: November 1, 2003
- Out Around RigelAuthor: Robert H. WilsonReleased on Project Gutenberg: February 10, 2007
- Out in the Forty-Five: Duncan Keith's VowAuthor: Emily Sarah HoltReleased on Project Gutenberg: December 7, 2007
- Out Like a LightAuthor: Randall Garrett, Laurence M. Janifer, Kelly FreasReleased on Project Gutenberg: January 28, 2008
- Out of Doors—California and OregonAuthor: J. A. (Jackson Alpheus) GravesReleased on Project Gutenberg: March 1, 2004
- Out of the AshesAuthor: Ethel Watts Mumford GrantReleased on Project Gutenberg: August 25, 2004
- Out of the deepAuthor: Charles Kingsley, Frances Eliza Grenfell KingsleyReleased on Project Gutenberg: January 8, 2007
- Out of the Fog: A Story of the SeaAuthor: Charles K. (Charles Kellogg) OberReleased on Project Gutenberg: April 1, 2005
- Out of the PrimitiveAuthor: Robert Ames BennetReleased on Project Gutenberg: July 1, 2004
- Out of the Triangle: A Story of the Far EastAuthor: Mary E. (Mary Ellen) BamfordReleased on Project Gutenberg: January 1, 2003
- Out of Time's AbyssAuthor: Edgar Rice BurroughsReleased on Project Gutenberg: June 1, 1996
- Out To Win: The Story of America in FranceAuthor: Coningsby DawsonReleased on Project Gutenberg: February 27, 2005
- Out with Gun and Camera; or, The Boy Hunters in the MountainsAuthor: Edward StratemeyerReleased on Project Gutenberg: July 19, 2004
- Outdoor Sports and GamesAuthor: Claude Harris MillerReleased on Project Gutenberg: July 16, 2005
- Outline of the development of the internal commerce of the United States: 1789-1900Author: Thurman William Van MetreReleased on Project Gutenberg: May 24, 2008
- Outlines of a mechanical theory of stormsAuthor: Thomas BassnettReleased on Project Gutenberg: July 8, 2006
- Outlines of English and American Literature: An Introduction to the Chief Writers of England and America, to the Books They Wrote, and to the Times in Which They LivedAuthor: William J. (William Joseph) LongReleased on Project Gutenberg: March 1, 2005
- Outlines of Greek and Roman MedicineAuthor: Elliott, James, SirReleased on Project Gutenberg: May 5, 2007
- Outlines of Lessons in Botany, Part I; from Seed to Leaf: For the Use of Teachers, or Mothers Studying with Their ChildrenAuthor: Jane Newell MooreReleased on Project Gutenberg: January 1, 2004
- Outlines of the Earth's History: A Popular Study in PhysiographyAuthor: Nathaniel Southgate ShalerReleased on Project Gutenberg: June 12, 2006
- Outlines of Universal History, Designed as a Text-book and for Private ReadingAuthor: George Park FisherReleased on Project Gutenberg: September 1, 2005
- OutpostAuthor: Jane G. (Jane Goodwin) AustinReleased on Project Gutenberg: November 1, 2003
- Outspoken EssaysAuthor: William Ralph IngeReleased on Project Gutenberg: March 4, 2005
- Outward Bound Or, Young America Afloat: A Story of Travel and AdventureAuthor: Oliver OpticReleased on Project Gutenberg: May 27, 2005
- Outwitting our nervesAuthor: Josephine A. (Josephine Agnes) Jackson, Helen M. SalisburyReleased on Project Gutenberg: February 8, 2005
- Over HereAuthor: Edgar A. (Edgar Albert) GuestReleased on Project Gutenberg: September 2, 2005
- Over Paradise Ridge: A RomanceAuthor: Maria Thompson DaviessReleased on Project Gutenberg: March 3, 2005
- Over Prairie TrailsAuthor: Frederick Philip GroveReleased on Project Gutenberg: July 1, 2004
- Over Strand and Field: A Record of Travel through BrittanyAuthor: Gustave FlaubertReleased on Project Gutenberg: December 2, 2004
- Over the Border: Acadia, the Home of "Evangeline"Author: Chase, Eliza B. (Eliza Brown)Released on Project Gutenberg: October 1, 2004
- Over the Fireside with Silent FriendsAuthor: Richard KingReleased on Project Gutenberg: April 20, 2008
- Over the PassAuthor: Frederick PalmerReleased on Project Gutenberg: February 1, 2004
- Over the Rocky Mountains to AlaskaAuthor: Charles Warren StoddardReleased on Project Gutenberg: October 3, 2007
- Over the Rocky Mountains: Wandering Will in the Land of the RedskinAuthor: R. M. (Robert Michael) BallantyneReleased on Project Gutenberg: December 31, 2007
- Over the Side: Captains All, Book 6.Author: W. W. (William Wymark) Jacobs, Will OwenReleased on Project Gutenberg: February 1, 2004
- Over the SliprailsAuthor: Henry LawsonReleased on Project Gutenberg: May 1, 1998
- Over the TeacupsAuthor: Oliver Wendell HolmesReleased on Project Gutenberg: September 29, 2004
- Over the Top With the Third Australian DivisionAuthor: G. P. (George Percival) Cuttriss, Monash, John, Sir, Neil McBeathReleased on Project Gutenberg: August 24, 2005
- Over There: War Scenes on the Western FrontAuthor: Arnold BennettReleased on Project Gutenberg: March 1, 2004
- OverbeckAuthor: J. Beavington AtkinsonReleased on Project Gutenberg: April 15, 2008
- Overdue: The Story of a Missing ShipAuthor: Harry Collingwood, W. Herbert (William Herbert) HollowayReleased on Project Gutenberg: April 13, 2007
- Overland Red: A Romance of the Moonstone Cañon TrailAuthor: Henry Herbert Knibbs, Anton Otto FischerReleased on Project Gutenberg: November 11, 2006
- Overland through Asia; Pictures of Siberian, Chinese, and Tartar LifeAuthor: Thomas Wallace KnoxReleased on Project Gutenberg: October 20, 2004
- Overland: A NovelAuthor: John William De ForestReleased on Project Gutenberg: May 1, 2004
- OverruledAuthor: Bernard ShawReleased on Project Gutenberg: March 1, 2003
- Owen Clancy's Happy Trail; Or, The Motor Wizard in CaliforniaAuthor: Burt L. StandishReleased on Project Gutenberg: January 1, 2008
- Owen Hartley; or, Ups and Downs: A Tale of Land and SeaAuthor: William Henry Giles KingstonReleased on Project Gutenberg: February 3, 2008
- Owindia : a true tale of the MacKenzie River Indians, North-West AmericaAuthor: Charlotte Selina BompasReleased on Project Gutenberg: October 1, 2004
- OxfordAuthor: Andrew LangReleased on Project Gutenberg: December 1, 2000