- O Jogo da Fuga
- O Reino do Meio: Dois Irmãos
- O Reino do Meio: O Mal Interior
- O Retrato Cinza de Dorian
- O Sol Brilhante Demais
- Obertura
- Oblio
- Observation
- Obsolescence
- Occupy Space
- Occupy Stinking America
- Oceanspace
- Octavia Gone
- October the First Is Too Late
- Octopusgarden
- Odyssee der Sternfahrer: Science Fiction Sammelband
- Of a Strange World Made
- Of Kindness and Kilowatts (Nothing is Promised 3)
- Of Two Minds
- Off the Face of the Earth
- Offenbarung
- Oklahoma Salvage
- Old Man's War
- Old Side of Mars
- Old Twentieth
- Olympos
- Olympus Mons
- Ombre di plastica
- Omega
- Omega Empire
- OmniWar: Anunnakx
- OmniWar: Omicron
- On a Forsaken Land Found
- On the Beach
- On to the Asteroid
- One Against the Moon
- One Awake in All the World
- One in 300
- One Last Goodbye
- One Way
- Only Human
- Onset, Reset, Mindset
- Operation: Outer Space
- Ophir. Codice vivente
- Oppy
- Opt Out
- OPTI. MYSTIC
- Ora et labora. Повесть о послушнике Иакове, Святой Инквизиции и таинственных кругах на полях
- Oral Argument
- Orb World of the Dragon
- Orbital Cloud
- Orbital Lily
- Orbus
- Ordnance
- Orgoglio e sacrificio
- Oriel, the Arctic Queen
- Original Strand
- Origins
- Original Strand
- Origins
- Orion Shall Rise
- Orlo's Orbits
- Orphaned Voices
- Orphans of the Sky
- Os Reis do Rio
- Ossian's Ride
- Otekah - Das Sonnenmädchen
- Other Americas
- Otherworld
- Our Child of Two Worlds
- Our Dependence on Foreign Keys
- Our Lady of Holy Death
- Our Once Warm Earth
- Ouroboros
- OUT OF BOUNDS
- Out of Era
- Out of the Box
- Out of the Dead City
- Out Of The Silent Planet
- Out of the Sun
- Out of This World Adventures
- Out of Time: A Time Travel Novel
- Outcast
- Outermost
- Outpost
- Outpost Omega Seven