- O Dia Da Sua Chegada
- O Paradoxo da Garota da Ponte
- O Pedido Cintilante
- O Peso da Honra (Reis e Feiticeiros – Livro 3)
- O Presente da Batalha (Livro # 17 Da Série: O Anel Do Feiticeiro)
- O Relojoeiro: um conto
- O saci epaminondas
- O telephone
- O timbre
- O Vírus da Múmia
- Oaklade
- Oasis
- Oasis – The Last Humans
- Oathsworn
- Obernewtyn
- Oblivion
- Observation Day
- Observer
- Obsidian
- Obsidian (Ember book 2)
- Obřad Mečů (Sága Čarodějův Prsten – Kniha Sedmá)
- OCDaniel
- Ocean City - Tome 1 - Chaque seconde compte
- Ocean City - Tome 2 - Dans la cachette des rebelles
- Ocean Depths
- Oceans of Red: Demon Revolution
- Odd One Out
- Ode to Rebellion
- Odiosis
- Odissea nel futuro
- Of Dreams and Rust
- Of Gaea
- Of Jenny and the Aliens
- Of One Skein
- Off Balance
- Off on a Comet
- Off On A Comet Or Hect Or Servadac
- Off Planet
- Offshoots
- Ofiara Broni (Księga 8 Kręgu Czarnoksiężnika)
- Og noget andet er -
- Oh My Goth
- Ojos de Lechuza
- Okul Da Vampir Hayatı :Türk
- Old Glory
- Old Magic
- Old Stone Face
- Olga and the Smelly Thing from Nowhere
- Olga Romanoff or, The Syren of the Skies
- Olga: Out of Control!
- Olga: We're Out of Here!
- Olhos de Fogo
- Oli, A Very New Moon
- Oliver and Charley -Supersenders
- Olivia's Escape
- Oltre i confini di Hìndamoor
- Omega
- Omega City
- Omega City: Infinity Base
- Omega City: The Forbidden Fortress
- Omnidisk
- Omvänd (Bok #1 i Vampyrjournalerna)
- On Congratulon
- On Destiny
- On Mission
- On Pointe All Day Long
- On the Edge of Gone
- On the Eighth Tin
- On The Flip Side
- On Thin Ice
- On Top of the World
- Once We Were
- Ondinas (Serie Elementales)
- One Chance
- One Crow Alone
- One Giant Leap
- One if by Land, Two if by Submarine
- One Last Look: a postapocalyptic YA short story (Bunker Story #1)
- One of a Kind
- One of Many in the Universe
- One of the Girls
- One Small Step
- One Wish Away
- Ones and Zeroes
- Only a Monster
- Only So Big
- Only You Can Save Mankind
- Onurun Bedeli (Krallar ve Büyücüler—3. Kitap)
- Onyx Elixir
- Opal
- Opaque: Scion Saga Book 1
- Operation Columbus
- Opaque: Scion Saga Book 1
- Operation Columbus
- Operation Do-Over
- Operation Red
- Operation Stargazer
- Operation: Montauk
- Opposite of Always
- Opposition
- Orbital Hotel
- Orienteer
- Origin
- Origins (Endgame: The Training Diaries, Volume 1)
- Origins of Dark Angel
- Orion Gambit
- Orleans
- Ormog
- Orphan Dreamer and the Glass Tattoo
- Orphan Dreamer and the Missing Arrowhead
- Orphan Station
- Orphans of the Celestial Sea, Episode 2: Engine Trouble
- Orphans of the Sky
- Orthicon
- Osud Draků (Sága Čarodějův Prsten – Kniha Třetí)
- Other Times, Other Spaces: A Short Story Collection
- Other Worlds Than These
- OtherEarth
- Otherplace
- Otherworld
- Otra vez el Santo
- Our Architect
- Our Monsters
- Out of Gas
- Out of the Box
- Out of the Shadows
- Out Of The Silent Planet
- Out of the Soup (4)
- Out of This World
- Out of Time
- Out There: Book Five: The Clan Wars
- Out There: Book Four: Earth
- Out There: Book One: Paradise
- Out There: Book Three: TiWat
- Out There: Book Two: Adonae
- OuterSphere (The Rayne Trilogy #2)
- Outliers