- Operation Schneewolf
- Operation Seewespe
- Operation Selector
- OPERATION SIBIRIEN
- Operation sjöhästen
- Operation Starfire
- OPERATION SYRIEN
- Operation Underworld
- Operation Vergangenheit
- Operation Wolf Hunt
- Operation Zenvox
- Operation: Deepcover
- Operation: Bloodhound
- Operation: Blue Christmas
- Operation: Outer Space
- Operative 66
- Operazione Fritham
- Operazione reset
- Operação Cambess
- Operený had
- Ophelia & Lyan Are Dead Meat
- Ophelia, Demons & Money
- Ophelia, le vite di una ghost writer. Inconfessabili segreti
- Ophelia, le vite di una ghost writer. Inquietanti rivelazioni
- Ophelians
- Opium Dream
- Opium Poppy
- Opkaldet
- Opowieści niezwykłe
- Oppergeest Beer
- Opposing Forces
- Opposite Land
- Optimizing America
- Opting In
- Opus Dei
- Opération : Soleil de Jade
- Or gris en Algérie
- Or She Dies
- Or3
- Ora Pro Nobis
- Ora Pro Nobis
- Ora saremo liberi
- Ora zero
- Oracle
- Oracle - Cure The World - Pangaea (Vol. 7)
- Oracle - Fire Island (Vol. 2)
- Oracle - Mutant Wood (Vol. 5)
- Oracle - River of Ore (Vol. 3)
- Oracle - Solar Wind (Vol. 4)
- Oracle - Sunken Earth (Vol. 1)
- Oracle Inception
- Oracle's Legacy: Children of Sun (Book 1)
- Oracle's Legacy: Dawn of Illumination (Book 3)
- Oracle's Legacy: Shadows of Fate (Book 2)
- Oracoli
- Orange and Green
- Orange Crush
- Orangen und Datteln
- Orangen und Datteln - Jubiläumsedition zum 101. Todesjahr von Karl May
- Orb Sceptre Throne
- Orb World of the Dragon
- Orbianna: The City Beneath the Sea
- Orbit
- Orbus
- ORCA - Jasons Traum
- Orchids in Moonlight
- Ordeal at the Old Ivy Oak
- Order
- Order and Mrs Cohen's Conviction
- Order att döda
- Order of the Seers
- Order of the Seers: The Last Seer
- Order of the Seers: The Red Order
- Order-Born
- Orders is Orders
- Ordinary
- Ordinary Wolves
- Ordnance
- Ordon
- Ore giapponesi
- Oregonian Nights
- Orei
- Orfanii
- Orgullo y prejuicio
- Oria’s Rippin Adventure
- Oriental Tales for the Entertainment of Youth Selected from the Most Eminent English Writers
- Orientzyklus
- Origami
- Origem da Sombra
- Origin Exposed
- Original Intent
- Original Sins
- Originals Ride
- Origines obscures...
- Origins
- Origins (The Legionnaire, #1)
- Origins of the Black Idol
- Origins Of The Magdon: The Journey Ahead
- Origins Of The Magdon: Valley Of The Kings
- Origins Of The Magdon: Valmiki Nagar
- Origins Of The Magdon: Vatican Archives
- Origins Of The Magdon: Vercovicium
- Origins: A Paranormal Thriller
- Orinoco
- Orion's Gift
- Orion: Suresh Adventure
- Orioni
- Orishadaon: To the Ends of the Urth
- Orissa
- Orizzonte
- Orlan & Byggvir
- Orlan & Bygvvir
- Orlando Furioso
- Orli Szpon
- Orltron V: The Syn of Paruti
- Ornamentum
- ORO
- Oro azul (Archivos NUMA 2)