- Opération Jabberwock
- Opération Lorelei
- Opération Sabines
- Opętana (Część 12 Wampirzych Dzienników)
- Or et Nuit
- Or Even Eagle Flew
- Or not to be
- Or What You Will
- Or, Sang, Soleil
- Oracle
- Oracle Adored
- Oracle Bones (Bookburners Season 3 Episode 6)
- Oracle Defiant
- Oracle Dream
- Oracle of Nightmares
- Oracle Quest
- Oracle V – Travels Through Other Dimensions
- Oracle's Fire
- Oracle's Moon
- Oracle, Clockwork Heart Tale No. 3
- Oracles of Aragret (a Steampunk Novel)
- Oracoli
- Oraculum Dei
- Oraisons
- Oran Roy
- Orange Crush
- Orange Glory: The Zoomins Must Die
- Orange Image
- Orange Storm
- Orange Thief
- Orb
- Orb and Arrow, Book I: Exploration
- Orb of Light
- Orb of Souls
- Orb Rider: Angel of Shadows
- Orb Sceptre Throne
- Orbe, cetro, trono
- Orbias
- Orbias - o Demónio Branco
- Orbis Onirika Primo Volume
- Orbital Lily
- Orbs of Avalon: Tales of Urban Magick and Horror
- Orbs of Avalon: Tales of Urban Magick and Horror
- Orbs of Azure
- Orc Eroica, Vol. 1 (light novel)
- Orc Eroica, Vol. 2 (light novel)
- Orc Haven
- Orc In Winter
- Orc Warfare
- Orca World
- Orchid & The Great Nudini
- Orchidaceous: Exsanguinate Book 1
- Orchideen
- Orconomics
- Orcs: Army of Shadows
- Orcs: Bad Blood
- Orcs: Inferno
- Orcslayer
- Orcus Cave
- Orcus Unchained
- Ordeal of the Dragon
- Ordem vermelha
- Order in Chaos
- Order of Bogdan Khmelnitsky
- Order of Britain: The Devil's Regiment
- Order of Earth
- Order of Fire
- Order of Rings: Uncommon Synths
- Order of Seven
- Order Of The Black Sun
- Order of the Blade Boxed Set (Books 1-4)
- Order of the Dragon
- Order of the Hunt
- Order of the Lily
- Order of the Lily, the Complete Series
- Order Restored
- Order-Born
- Ordermaster
- Ordinary Joe and the Mark of Four
- Ordinary Miracles
- Ordinary Monsters
- Ordinary People's Miracles
- Ordinary Wonders: A Fantasy Short Story Collection
- Ordination
- Ordon
- Oregon Elsewise: Eight short stories of an Oregon that never was
- Orejas
- Orescu: La triolgía de Thundra
- Orgasms
- Ori Miradha (La Ricerca)
- Ori Mirhada - Tradimenti e Sogni Infranti
- Oria's Enchantment
- Oriam
- Orian
- Oriana
- Oriana's Eyes
- Orient Fevre
- Oriental Tales for the Entertainment of Youth Selected from the Most Eminent English Writers
- Oriente de perla
- Origami
- Origem da Sombra
- Origem Mortal
- Origin
- Origin ARS 1
- Origin ARS
- Origin ARS 3
- Origin ARS 4
- Origin ARS 5
- Origin ARS 6
- Origin ARS 7
- Origin Exposed
- Origin of an Oracle, A Rai Saga Short Story
- Origin of Darkness (Daeva, #2)
- Origin of Echoes: Book Two of the Elese Saga
- Origin of Pietas
- Origin of the Grim Reaper
- Origin of the New Dawn
- Origin of the Succubus
- Origin Phase Cycle Box Set
- Origin Scroll (Targa Trilogy #1)
- Original Bedside Stories Book 1
- Original Grace
- Original Sin
- Original Sinner