- O Atraso
- O Brave New World: Teilhard's Prophecy
- O caminho da verdade: Uma história no apogeu do povo verdadeiro
- O Despertar de um Rownsder
- O entrelaçamento electroquântico de que são feitas as lendas (Comandante Serralves)
- O Escritor
- O Escritor (Português Do Brasil)
- O Espantoso Mundo da Antecipação
- O Fim Do Mundo
- O Fim do Mundo
- O For God's Sake
- O Fortuna: Lower Heaven, Episode Two
- O Glorioso incorporado: As Crónicas de Joshua
- O Incrível Congresso de Astrobiologia
- O interrogador
- O jardim cosmogônico
- O Jogo da Fuga
- O meu irmão é um marginal - Livro 2 Liberdade
- O mistério de Troia
- O Negative
- O planeta vermelho
- O Portal da Pirâmide
- O Primmeiro Contacto
- O psicanalista de robôs
- O Reino do Meio: Dois Irmãos
- O Reino do Meio: O Mal Interior
- O Retrato Cinza de Dorian
- O Sol Brilhante Demais
- O viajante do tempo
- O Viajante do tempo e a Princesa
- O xenólogo de Sírius
- O Življenju, Vesolju in sploh Vsem
- O'Ceagan's Legacy
- O'Mally's Station
- O'Sheen's Photo Finish
- Oak Ridge
- Oaken
- Oarsman of the Princess
- Oasi
- Oasis
- Oasis (Les Derniers Humains : Tome 1)
- Oasis 6: Medallion of Blood
- Oasis One
- Oasis Tales of the Conjuror: and other stories
- Oath Bound: Book V of the Order of the Air
- Oath of Fealty
- Oaths and Miracles
- Oaths of Legacy
- Obertura
- Obi-Wan Kenobi: Ramblings of a Crazy Old Hermit
- Obiekt 271
- Objects of Wrath
- Obligations of Blood
- Oblio
- Oblivion - Tome I
- Oblivion Flight: A Military Science Fiction Space Opera Epic (The Oblivion Saga Book 2)
- Oblivion Gambit: A Military Science Fiction Space Opera Epic (Book 4)
- Oblivion Gate Episode Four
- Oblivion Gate Episode One
- Oblivion Gate Episode Three
- Oblivion Gate Episode Two
- Oblivion Gate: The Complete Series
- Oblivion Quest: A Military Science Fiction Space Opera Epic (Book 3)
- Oblivion Threshold: A Military Science Fiction Space Opera Epic (The Oblivion Saga Book 1)
- Oblivionlore Volume I
- Oblivious Demon
- OBLIX: The Summoning
- Obluvium: Sanctuary
- Obras Maestras de Julio Verne
- Observation
- Obsession
- Obsessions: An Anthology of Original Fiction
- Obsidian Detective
- Obsidian Fire: Revelations of a Secret Brotherhood
- Obsidian Fire: The Cave of the Sleeping Sword
- Obsidian Prey
- Obsidian Tears
- Obsidian Worlds: 11 Mind-Bending Sci-Fi Shorts
- Obsidian's Child
- Obviously, Aliens
- Occam's Laser
- Occupied Earth
- Occupied Origins
- Occupy Space
- Occupy Stinking America
- Ocean Untamed
- Oceanic
- OCEANS: The Anthology
- Oceanspace
- Oceanus: Living In Isolation
- Ochi Goi
- Octagla 1: Slingshot Play
- Octagla 2: Rematch
- Octavia Gone
- Octavius Mint and the Indigo Dragon
- October 9th
- Octavius Mint and the Indigo Dragon
- October 9th
- October the First is Too Late
- Octopocalypse
- Octopusgarden
- Ocularis
- Odd Exam
- Odd Girl Out
- Odd John
- Odd John and Sirius
- Odd Numbers
- Odd, Strange and Curious
- Ode to Joy
- Oden
- Odette C. Bell Sci-Fi Bundle
- Odiabili resti
- Odin lándzsája
- Odin's Eye
- Odissea nel futuro
- Odjuren Hela bokserien
- Odregan #1
- Odregan #2
- Odyssee der Sternfahrer: Science Fiction Sammelband
- Odyssee in die Unendlichkeit: Raumschiff Rubikon Band 1-8: Science Fiction Abenteuer Paket
- Odyssey
- Odyssey Bourne Force
- Odyssey in Space
- Odyssée
- Odyssées chimériques
- Oeps!
- Of A Darker Void (Asterion Noir Book 2)
- Of a Strange World Made
- Of All Possible Worlds
- Of Cinder and Bone
- Of Crimson Indigo
- Of Dawn and Embers
- Of Dust and Sand
- Of Fire and Night
- Of Flesh and Feathers
- Of Gods and Globes
- Of Gods Strangers and Messengers
- Of Jackals and Crusaders
- Of Kindness and Kilowatts (Nothing is Promised 3)
- Of Kings, Queens and Colonies: Coronam Book I
- Of Love, Free Will, and Gray Squirrels on a Summer Evening
- Of Machines and Men
- Of Myth And Monster