- Opening The Moonlight Gate
- Openings (Book One of The Pawn's Game)
- Operace Thümmel
- Operació Gesaleic o Diari d'un viatge
- Operacja "Thor" (Saga Sięgając poza horyzont)
- Operation
- Operation "The Black Thunder"
- OPERATION AMAZONAS
- OPERATION ANTARKTIKA
- Operation Arcana
- Operation Arche / Der Krieg der Ketzer
- Operation Ark: A Project Enterprise Story
- OPERATION ARKTIS
- Operation Artemis
- Operation Bigfoot
- Operation Breakout: Merkiaari Wars 4
- Operation Castus
- Operation Catskill: An Oblivion Saga Prequel (The Oblivion Saga Book 0)
- Operation Chaos and Operation Luna
- Operation Chupacabra
- Operation Cobalt
- Operation Code Named Sushi!
- Operation Compelling
- Operation D3
- Operation De-ICE (The Battle for Earth)
- Operation Deep Thaw
- Operation Disaster
- Operation Donnerschlag
- Operation Earthworm
- Operation Exile
- Operation Fox
- Operation Fury
- Operation GOTCHA: The Soviet Union's Top-Secret Plan to Launch a Surprise Cruise Missile Attack Agai...
- Operation Grendel
- Operation Iago
- Operation Interstellar (Serapis Classics)
- Operation Interstellar and seven more Stories
- Operation Isis
- Operation JFK
- OPERATION LOCH NESS
- OPERATION LONDON (Outbreak 2)
- Operation Longlife
- Operation Mauerfall
- Operation Mermaid: The Project Kraken Incident
- Operation Misfit
- Operation Motherland
- Operation Noah's Ark
- Operation Oracle: Merkiaarri Wars 3
- Operation Outer Space
- Operation Phoenix
- Operation Phoenix Book 1: We're Not Alone
- Operation Phoenix Book 2: Bohina
- Operation Phoenix Book 3: Imperial Guard
- Operation Phoenix Book 4: Invasion
- Operation Rabbit Hole
- Operation Razmer
- Operation Retribution Trilogy
- Operation Retribution: Luring the Prince into the Open
- Operation Retribution: Taking the Fight Off World
- Operation Retribution: The Training Phase
- Operation Rubber Ducky
- Operation sammetsvind
- Operation Sasquatch: The Piñon Paradox
- Operation Save Mars
- Operation Schattenbrecher
- OPERATION SIBIRIEN
- Operation Sleeping Dragon
- Operation Starseed
- Operation Sunset
- OPERATION SYRIEN
- Operation Terra 2.0
- Operation Terror (Serapis Classics)
- Operation Trojan
- Operation Underworld: The Complete Trilogy
- Operation Unthinkable: The Adventures of Air Group Captain Sebastopol Valiant
- Operation Venus
- Operation Vermont
- Operation Vildkatt
- Operation Z-Day (The Raven Falconer Chronicles: Episode One)
- Operation: black Eagle - Operação: águia Negra
- Operation: Capture Cyborg!
- Operation: Endgame
- Operation: Montauk
- Operation: Save America
- Operazione drago
- Operazione Genesi
- Operazione Manhattan
- Operazione Pettirosso
- Opfermond - Ein Fantasy-Thriller
- Ophal
- Ophannim Eye
- Ophelia & Lyan Are Dead Meat
- Ophelia Immune
- Ophelia In My Arms
- Ophelia Omarmd
- Ophelia Scale - Die Welt wird brennen
- Ophelia's Husband
- Ophelia, Demons & Money
- Ophelia, le vite di una ghost writer. Ambiguità occulte
- Ophelia, le vite di una ghost writer. Perversioni d'autore
- Ophid Dei
- Ophir. Codice vivente
- Ophis
- Ophiuchus Cube
- Ophiuchus Cube Book 1
- Ophéa - Im Bann des Drachen
- Opiniile unui călător nedemn de încredere
- Opičí král
- Opnieuw en opnieuw en opnieuw
- Opojení až za hrob
- Opon-Hul
- Opoponax Dreams
- Opostos
- Opowiadania najlepsze
- Opowiadania prawie wszystkie
- Opowiadania zebrane, tom 1
- Opowiadania zebrane, Tom 2
- Opowieści celtyckie Tom IV
- Opowieści celtyckie. Tom 1
- Opowieści celtyckie. Tom 2
- Opowieści celtyckie. Tom 3
- Opowieści nadzwyczajne (Tom I/Tom II)
- Opowieści niesamowite. Mystery Tales
- Opowieści o pilocie Pirxie
- Oppenheimer Blues
- Opportunity Calls Chinavare's Find Book 1
- Opportunity Calls: Chinavare's Find Book One
- Opportunity Found
- Oppose
- Opposite Land
- Opposite Reaction
- Opposites Do Atrract
- Opposition
- Oppositum
- Oppressed: Cursed Ones 2
- Opprobrium
- Oppvåkningen
- Oppy
- Oprawca boży
- Oprosti
- Opskurno
- Opstandeling, Pion, Koning (Over Kronen en Glorie—Boek 4)
- Opt Out
- OPTI. MYSTIC