| One-Kuri-WayLightning Overdrive · 065 | Lightning Overdrive | 065 | Common | €0.06 |
| One or EightPhantom Rage · 080 | Phantom Rage | 080 | Common | €0.03 |
| One-Shot WandAbyss Rising · 051 | Abyss Rising | 051 | Common | $0.13 |
| One-Time PasscodeCircuit Break · 061 | Circuit Break | 061 | Rare | €0.07 |
| One-Way SynchroLegendary 5D's Decks · 06 | Legendary 5D's Decks | 06 | New | €0.14 |
| One Who Hunts SoulsUnlisted Printings | Unlisted Printings | — | — | — |
| Onibimaru Soul SweeperBattle of Chaos · 046 | Battle of Chaos | 046 | Common | €0.07 |
| Oni-Gami ComboGeneration Force · 060 | Generation Force | 060 | Common | €0.09 |
| OnikujiMaximum Crisis · 099 | Maximum Crisis | 099 | Common | €0.03 |
| Oni Tank T-34Pharaoh's Servant · 059 | Pharaoh's Servant | 059 | Common | €0.08 |
| OnmorakiGhosts From the Past: The 2nd Haunting · 032 | Ghosts From the Past: The 2nd Haunting | 032 | Ultra Rare | €0.10 |
| OnomatokageDoom of Dimensions · 007 | Doom of Dimensions | 007 | Common | €0.10 |
| OnomatopairaLegacy of the Valiant · 067 | Legacy of the Valiant | 067 | Rare | €0.09 |
| OnomatopiaWorld Superstars · 024 | World Superstars | 024 | Prismatic Secret Rare | €0.02 |
| OnomatopickupLegendary Duelists: Magical Hero · 037 | Legendary Duelists: Magical Hero | 037 | Rare | €0.17 |
| Onslaught of the Fire KingsOnslaught of the Fire Kings Structure Deck · 022 | Onslaught of the Fire Kings Structure Deck | 022 | Super Rare | €0.15 |
| On Your Mark, Get Set, DUEL!Maze of Memories · 016 | Maze of Memories | 016 | Super Rare | €0.05 |
| OoguchiMetal Raiders · 032 | Metal Raiders | 032 | Short Print | €0.05 |
| OokaziStarter Deck: Kaiba · 023 | Starter Deck: Kaiba | 023 | Common | €0.09 |
| Oops!Extreme Force · 080 | Extreme Force | 080 | Short Print | €0.06 |
| O - OversoulEnemy of Justice · 041 | Enemy of Justice | 041 | Common | €0.07 |
| Opening of the Spirit GatesStructure Deck: Sacred Beasts · 020 | Structure Deck: Sacred Beasts | 020 | Common | €0.02 |
| Opera the Melodious DivaClash of Rebellions · 008 | Clash of Rebellions | 008 | Common | €0.02 |
| Oppressed PeopleMagician's Force · 002 | Magician's Force | 002 | Common | €0.19 |
| Opti-Camouflage ArmorAncient Sanctuary · 035 | Ancient Sanctuary | 035 | Short Print | €0.50 |
| OpticlopsLegacy of Darkness · 009 | Legacy of Darkness | 009 | Rare | €0.04 |
| Option HunterShadow of Infinity · 058 | Shadow of Infinity | 058 | Rare | €0.18 |
| Option TokenOTS Tournament Pack 20 · 027 | OTS Tournament Pack 20 | 027 | Super Rare | €0.18 |
| Oracle of the HeraldThe New Challengers · 066 | The New Challengers | 066 | Common | €0.09 |
| Oracle of the SunAbsolute Powerforce · 019 | Absolute Powerforce | 019 | Super Rare | €0.09 |
| Oracle of ZefraCrossed Souls · 060 | Crossed Souls | 060 | Secret Rare | €0.07 |
| Orbital 7Cosmo Blazer · 020 | Cosmo Blazer | 020 | Super Rare | €0.09 |
| Orbital BombardmentPower of the Duelist · 053 | Power of the Duelist | 053 | Common | €0.05 |
| Orbital HydralanderCode of the Duelist · 035 | Code of the Duelist | 035 | Common | €0.07 |
| Orb of YasakaThe Duelist Genesis · 055 | The Duelist Genesis | 055 | Common | €0.06 |
| Orca Mega-Fortress of DarknessInvasion of Chaos · 084 | Invasion of Chaos | 084 | Super Rare | €0.21 |
| Orcust Brass BombardSoul Fusion · 014 | Soul Fusion | 014 | Rare | $0.19 |
| Orcust CrescendoDark Neostorm · 074 | Dark Neostorm | 074 | Super Rare | €0.15 |
| Orcust Cymbal SkeletonSoul Fusion · 015 | Soul Fusion | 015 | Rare | €0.30 |
| Orcust Harp HorrorSoul Fusion · 016 | Soul Fusion | 016 | Rare | €0.23 |
| Orcust KnightmareSavage Strike · 021 | Savage Strike | 021 | Common | €0.02 |
| Orcustrated AttackSoul Fusion · 070 | Soul Fusion | 070 | Common | €0.05 |
| Orcustrated BabelSoul Fusion · 057 | Soul Fusion | 057 | Rare | $0.24 |
| Orcustrated CoreSoul Fusion · 071 | Soul Fusion | 071 | Common | €0.05 |
| Orcustrated EinsatzSoul Fusion · 059 | Soul Fusion | 059 | Common | €0.11 |
| Orcustrated ReleaseSavage Strike · 076 | Savage Strike | 076 | Common | €0.06 |
| Orcustrated ReturnSoul Fusion · 058 | Soul Fusion | 058 | Secret Rare | $0.24 |
| OrcustrionSoul Fusion · 045 | Soul Fusion | 045 | Ultra Rare | $0.79 |
| Ordeal of a TravelerPharaonic Guardian · 042 | Pharaonic Guardian | 042 | Short Print | $0.14 |
| Order of the QueenSpeed Duel GX: Duelists of Shadows · 12 | Speed Duel GX: Duelists of Shadows | 12 | Common | $0.07 |