- One with Bird
- Only Disconnect
- Only In A Dream Series
- Only the Moon: A Short Story Collection
- Only Wolf's Christmas
- Oona: A Fairy Tale
- Operation Arcana
- Ophannim Eye
- Ophelia In My Arms
- Ophelia Omarmd
- Opon-Hul
- Oracle, Clockwork Heart Tale No. 3
- Orange Thief
- Orchideen
- Orcs
- Orcs Bad Blood I
- Orcs Bad Blood II
- Orcs Bad Blood III
- Order in Chaos
- Order of the Blade Boxed Set (Books 1-4)
- Ordinary Wonders: A Fantasy Short Story Collection
- Oregon Elsewise: Eight short stories of an Oregon that never was
- Orgasms
- Origin
- Origin of an Oracle, A Rai Saga Short Story
- Orin
- Orin
- Ornaments
- Ornery Oldtimers
- Orsinian Tales
- Orwell m'a tu
- Os diabinhos da cozinha e outros contos sombrios
- Os Risos de Ema
- Oscar Rat's Secret Missions
- Ostatni bierze wszystko
- Other Aliens
- Other Realms: Volume One
- Other Realms: Volume Three
- Other Worlds, Better Lives
- OtherPlace
- Otherworld Chills
- Otherworld Nights
- Otherworld Secrets
- Otherworldly Maine
- Otherworlds
- OTIS ADELBERT KLINE Ultimate Collection: Science-Fantasy Classics, Sword & Sorcery Tales
- Our Cousin Trip Shorts Journal Smashup Including Bonus Journal 10
- Our First Halloween 2017
- Our Rainmaker
- Our Sunset Wall of Remembrance
- Ouroboros Ouzo
- Out of Curiosity
- Out of Darkness
- Out Of Here
- Out of Order Detective
- Out of the Dark
- Out of the Darkness
- Out of the Light
- Out of the Vaults
- Out of the Woods
- Out of the World : Sci-fi Menage Romance Collection
- Out Of This World
- Out of This World
- Out of This World: Queer Speculative Fiction Stories
- Out of Time: An Adventure of The Spectre
- Out of Tune
- Out of Uca
- Outlaw Pizza
- Outoja tarinoita
- Outside the Walls
- Over The Darkened Landscape
- Over the Hills and Far Away
- Over The Horizon
- Overheard in Fairyland
- Owl Light
- Oz: The Complete Collection