| Map | Title | Author | Players | |
|---|---|---|---|---|
| DM-Obedience-M7 | Obedience-M7 | Unknown | Unknown | |
| DM-Obliviation | DM-Obliviation | oblivion100 | Unknown | |
| DM-Oblivion2008-SE | Oblivion2008-SE | Unknown | Unknown | |
| DM-Oblivion]I[ | DM-Oblivion]I[ | Dan "CPT Stewart" Rodriguez | 2 - 4 | |
| DM-Oblivion_Classic | DM-Oblivion_Classic | Unknown | Unknown | |
| DM-Obstructed_B1 | Obstructed_B1 | Unknown | Unknown | |
| DM-Oceanic | Oceanic | Unknown | Unknown | |
| DM-Oceanic]I[ | DM-Oceanic]I[ | Checker | s | |
| DM-Oceanside | Oceanside | Matt Lefevere | Unknown | |
| DM-Octagon | Octagon | Unknown | Unknown | |
| DM-Odysseus | Odysseus | Xermacor | Unknown | |
| DM-Odyssey | Odyssey | Michail 'Moloch' Levchinko | 8-16 | |
| DM-Old_Gods_of_the_New_World | Old_Gods_of_the_New_World | Michail 'Moloch' Levchinko | 2-16 | |
| DM-OldFactory | Old Factory | info | 4 to 12 | |
| DM-OmicronMadness | OmicronMadness | {TA}.MaXimus(); | 4 to 12 | |
| DM-OneVersusOne | OneVersusOne | Unknown | Unknown | |
| DM-Operation_Dawn_Red_Sky | Operation Dawn Red Sky | Drummerextro | 24 to 32 | |
| DM-OrbitalDebris | Orbital Debris | Lord Porksword | 8 to 20 | |
| DM-OrbitalDecay | Orbital Decay | Lord Porksword | 6 to 18 | |
| DM-OrbitalDeconstruction | Orbital Deconstruction | Lord Porksword | 4 to 16 | |
| DM-OriensForest | OriensForest | Alex A. Galuzin | 4 to 6 | |
| DM-Oscillation | Oscillation | Unknown | 8 to 12 | |
| DM-Osiris | Osiris | TKBS | 2 to 12 | |
| DM-Oukill@rena_One | Oukill@rena_One | Unknown | 4 to 16 | |
| DM-Ourea_Beta | Ourea Beta | Eric 'Marsfyre' Berger | 6 to 16 |