- Operazione drago
- Operazione Pettirosso
- Ophal
- Ophelia In My Arms
- Ophelia Omarmd
- Ophid Dei
- Ophir. Codice vivente
- Ophiuchus Cube Book 1
- Opowieści o pilocie Pirxie
- Opportunity
- Opposite Reaction
- Oppy
- Opt Out
- OPTI. MYSTIC
- Optical Orifice of the Beholder
- Opting Out and Other Departures
- Opting Out: A Story of the Road
- Options
- Options of Survival
- Opus 1 - Le Chant de l'Arbre-Mère
- Opus Aria
- Opus X Series Boxed Set One
- Opzione zero!
- Ora et labora. Повесть о послушнике Иакове, Святой Инквизиции и таинственных кругах на полях
- Ora i maestri muoiono
- Oracle
- Oracle - Waters Deep (Vol. 6)
- Oracle Inception
- Oracle's Child
- Oracular Operations
- Oral Argument
- Orange Cerlo
- Orange Glory: The Zoomins Must Die
- Orange Jules ~ Syntax Error
- Orange Storm
- Orb
- Orb World of the Dragon
- Orbital Cloud
- Orbital Decay
- Orbital Extraction
- Orbital Havoc
- Orbital Lily
- Orbital Maneuvers
- Orbitale Balance
- Orbitsville
- Orbitsville Departure
- Orbitsville Judgement
- ORBS: The Complete 3-Book Science Fiction Series
- Orbus
- Orca
- Orchid in the Void
- Orchid Island
- Order 66
- Order of the Fallen
- Order of the Seers
- Order of the Seers: The Last Seer
- Order of the Seers: The Red Order
- Orders to Leave
- Ordinary
- Ordinary Ace
- Ordnance
- Oregon Elsewise: Eight short stories of an Oregon that never was
- Organic Destiny
- Orgoglio e sacrificio
- Oriel, the Arctic Queen
- Orienteer
- Origen
- Origin
- Origin ARS
- Origin ARS 5
- Origin of Pietas
- Origin of Prometheus
- Origin of Species
- Origin Phase
- Original Grace
- Original Strand
- Originated Under Twin Suns
- Origine perdue
- Origines
- Origins
- Origins (Book 1)
- Origins of a Hero
- Origins of the New Breed of Super Hero
- Origins of the New Breed of Super Villain
- Origins: The Denisovan Trilogy, Book One
- Orillion Prime
- Orion Among the Stars
- Orion and the Conqueror
- Orion Arm
- Orion Effect
- Orion in the Dying Time
- Orion Tilt
- Orion, Femspec Issue 6.2
- Orion: la Fortezza (Urania)
- Orion, Femspec Issue 6.2
- Orion: la Fortezza (Urania)
- Orion: Suresh Adventure
- Orlo's Orbits
- Ornery Oldtimers
- Oroboro Island
- Orologeria
- Orotund: Collected Short Stories Volume Two
- OROVITZ. Operazione Cassiopea
- Orphan Brigade
- Orphan Star
- Orphan Stone
- Orphan's Gold
- Orphaned Voices
- Orphans of Space-Time
- Orpheus
- Orson Scott Card's InterGalactic Medicine Show
- Orta
- Orthogonal Procedures
- Orussian Quarantine
- Orussian Quarantine: OpenDyslexic Edition
- Orwell m'a tu
- Os carangonços de Riobaldo
- Os hóspedes
- Os Reis do Rio
- Os sete portais para o mundo dos mortos
- Os Sonhos de Ashlynn
- Oscar Wilde: The Complete Collection (Best Navigation) (A to Z Classics)
- Oscuridad
- Osiris
- Osiris Blood, Part One: Watcher of Storms
- OSMINDA
- Ostatni Honorowy
- Ostrov doktora Moreaua
- Osud Draků (Sága Čarodějův Prsten – Kniha Třetí)
- Otaku
- Otaku - A.I.-P.I.
- Otekah - Das Sonnenmädchen
- Other Arms Reach Out to Me
- Other Eyes Watching
- Other Realms: Volume Three
- Other Voices
- Other Worlds
- Other Worlds Other Wonders
- Other Worlds Than These
- Other Worlds, Better Lives