- O
- OO
- OO
- OOak
- OakOb
- ObeOBO
- ObrOce
- OceOch
- Och
- OctODE
- OdeODO
- odoOf
- OfOff
- OffOgr
- OgrOh
- OhaOis
- OisOka
- OkaOku
- OkuOlc
- OldOld
- OldOli
- OliOli
- OliOls
- OlsOma
- OmaOme
- OMFOn
- OnOne
- OneOne
- ONEOne
- oneOnk
- OnkOnT
- OntOor
- OorOpe
- OpeOpu
- OpuOra
- OraOrc
- OrcOrd
- OrdOrh
- OrhOri
- OriOrl
- OrlOrq
- OrqOrt
- OrtOsa
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- OscOsm
- Osn
- Otr
- OtrOtt
- OttOur
- OurOut
- OutOut
- OutOve
- OveOve
- OveOwe
- OweOxi
- OxiOze
- ozz
- Operation Mindcrime
- Operation Ratification
- Operation Sodasteal (kaj strife & slaney(in)famous)
- Opération Zéro
- Operation, The
- Operation, The (predecessor to mewithoutYou)
- Operator (Hard Rock Band)
- Operator Please
- Operator, Hello
- Operators (Canadian band)
- Operators, The (ska, from Indianapolis, IN)
- Operus
- Opeth (Swedish progressive metal/rock)
- Opgeduveld
- Opgezwolle (Dutch rap group)
- Opgezwolle feat. Vrieling, Bert
- Ophanin
- Ophelia Ragtime Orchestra
- Ophelia's Eye (Melodic death metal band from Switzerland)
- Opheliac
- Ophelias, The (psychedelic rock band from San Francisco)
- Ophelias, The (Cincinnati indie rock band)
- Ophidian (hardcore dj)
- Ophidian & Peacock, Dr.
- Ophidian & Playah, Tha
- Ophidian Ascension, The (Australian death metal)
- Ophidian I
- Ophidian Memory
- Ophis (Germany, Metal)
- Ophthalamia
- Opi the Hit Machine
- Opia (indie electronic group: Cole Citrenbaum, DJ Stanfill and colorthought)
- Opiate for the Masses
- Opick
- Opio (Opion Lindsey - US rapper, from Souls of Mischief)
- Opio del Mono
- Opium (Belgian all girl pop group)
- Opium Jukebox
- Opium Moon
- Opium Owl (heavy psych rock band from Riga, Latvia)
- OPIUM project (Russian electronic group)
- Opium Warlords
- Opiuo (Australian electronica / breakbeat artist)
- Opiuo feat. Gift of Gab & Syreneiscreamy
- OPLIAM
- OPM (1999–current US dub pop hip‐hop punk reggae group)
- OPM & Big B
- Opodebota
- Opossom (New Zealand)
- OPP
- Oppenheimer
- Oppenheimer Analysis
- Oppenheimer, Andy (member of Oppenheimer Analysis)
- Oppera
- Oppidan
- Oppidan (UK garage producer)
- Opposite The Other
- Opposites, The
- Opposites, The feat. Adje
- Opposites, The feat. Faberyayo & Sjaak
- Opposites, The feat. Hydroboyz & Adje
- Opposites, The feat. Probz, Mr
- Opposites, The feat. Probz, Mr.
- Opposites, The feat. Sef
- Opposites, The feat. Spasmatic
- Opposites, The met Yellow Claw
- Opposition of One
- Opposition, The (London post‐punk band)
- Oppressed, The (Welsh punk/oi)
- Oppressor (US technical death metal)
- Opprobre
- Opprobrium
- OPROER (Belgian indie rock band)
- Opshop
- Opskamatrists, The
- Opsomer, Barbara (Belgian singer)
- Opti-Pop
- Optic
- optic core (experimental electronic/dance producer)
- Optic Sink
- Optiganally Yours
- Optimo (UK techno duo)
- Óptimo (bachata group/artist)
- Optimus (US rapper, aka Jordy Towers)
- Optimus Rhyme (US nerdcore hip hop group)
- Optiv & BTK
- Optiv & BTK feat. Ryme Tyme
- Opuntia (solo project of Mexico City producer Camila de Laborde)
- Opus (Austrian band; track: “Live Is Life”)
- Opus & Ambros, Wolfgang
