- Obviously, Aliens
- Obédience
- Obłęd: powieść fantastyczna
- Obřad Mečů (Sága Čarodějův Prsten – Kniha Sedmá)
- Ocalić przyszłość
- Occam's Laser
- Occam's Razor
- Occasion
- Occasion for Disaster
- Occasion... For Disaster
- Occhi di Ghiaccio
- Occhi di Gufo
- Occhi nello spazio (Urania)
- Occhi verdi
- Occhi Vuoti
- Occhio di gatto (Urania)
- Occult Book of Shadows
- Occult for Instant Coffee
- Occult Suspense for Mothers Box Set
- Occultic;Nine
- Occultic;Nine Volume 2
- Occultic;Nine Volume 3
- Occupied Origins
- Occupied Space I - Windswept
- Occupied Space II - Like A Boss
- Occupy Me
- Occupy Space
- Occupy Stinking America
- Occurrence: Episode One
- Ocean and Time: Shackle of the Keeper
- Ocean Dwellers' Legend
- Ocean Gods, Roman Blades
- Ocean Light
- Ocean of Anger
- Ocean of Empathy
- Ocean of Fear (Kormak Book Six)
- Ocean of Grass: Petrellan Saga 1
- Ocean of Storms
- Ocean On Fire
- Ocean on Top
- Ocean Salt
- Ocean Song Trilogy
- Ocean Stories
- Ocean Storm : The Moonlight Saga 2
- Ocean Storm : The Moonlight Saga 2
- Ocean Untamed
- Ocean's Bride
- Ocean's Fire
- Ocean's Fury
- Ocean's Justice
- Ocean's Kiss
- Ocean's Rise
- Ocean's War
- Ocean's Widow
- Oceana
- Oceana the Futa Mermaid
- Oceanblue - Lügen der Rettung
- Oceanblue - Stimmen der Feinde
- Oceanen vid vägens slut
- Oceania
- Oceano di pietra
- Oceans & Potions
- Oceans In Oniah
- Oceans of Callisto
- Oceans of Fire
- Oceans Of Fire
- Oceans Of Time
- OCEANS: The Anthology
- Oceanus, Tale of Two Tides
- Oceanus: Living In Isolation
- Oceany Europy
- Oceanïc
- Ocelový příboj
- Oceľové žezlo
- Och jorden snurrar vidare
- Ocho relatos
- Ochre Dragon
- Ochránce
- Ocre Rouge
- Octagla 1: Slingshot Play
- Octagla 2: Rematch
- Octagla 3: Semifinals
- Octagon
- Octavia #1: The Gemini Ring
- Octavia #2: The Ice Caves
- Octavia - Der achte Kontinent
- Octavia - Univers parallèles
- Octavia Gone
- Octavia's Brood
- Octavia's Wake
- Octavian
- Octavie d'Urville, 1
- Octavie d'Urville, 2
- Octavie d'Urville, 3 : la porte des ténèbres
- Octavius Mint and the Indigo Dragon
- October 9th
- October Ballet
- October Falling: Baqash Origins
- October Nights 3
- October Sci-fi & Fantasy
- October Sky
- October Snow
- October the First Is Too Late
- October Throne
- October's Gone
- Octopied
- Octopocalypse
- Octopony (Poniworld Chronicles #7)
- Octopusgarden
- Ocularis
- Oculta
- Oculus
- Oculus Lunae
- Oczy pełne szumu
- Océane
- Od and Ed
- Od Magic
- Od Valinoru do Mordoru
- Odalisca (El Ciclo Barroco Vol. I)
- Odalisque
- Odd Apocalypse
- Odd Hours
- Odd Interlude
- Odd John
- Odd John and Sirius
- Odd John: A Story Between Jest and Earnest
- Odd Man In
- Odd Man Out
- Odd Numbers
- Odd Questions, Odder Answers