- O
- OO
- OO
- OOak
- OakObi
- ObiObt
- ObtOce
- OceOct
- OctOdd
- OddODM
- ODOOf
- OfOfn
- OfnOh
- OhOhm
- OhmOK
- OKOkm
- OKOOla
- OlaOld
- OldOli
- OliOll
- OllOly
- OlyOME
- OmeOMP
- OmpOnD
- OneONE
- ONEOne
- OneOnl
- OnlOOJ
- OojOpe
- OpeOpp
- OppOra
- OraOrc
- OrcOre
- OreOri
- OriOri
- OriOrp
- OrpOrs
- OrtOsa
- OsaOse
- OshOss
- OssOth
- OthOtt
- OttOur
- OurOut
- OutOut
- OutOve
- OveOvi
- OviOwl
- OwlOxy
- OyOzu
- OzuOZZ
- Open Up and Bleeds, The
- Open, The
- OpenBSD
- Openside
- Opensight (Metal)
- Opensouls
- Opera (Polish group)
- Opera (Italian hard trance project)
- Opera Australia
- Opera Diabolicus (Doom/Black/Death Metal Swedish Band)
- Opera Familia
- Opera IX
- Opera Magna
- OperaBabes
- Operación Triunfo (fake artist)
- Operación Triunfo 2017
- Operación Triunfo 2018
- Operación Triunfo, Academia
- Operadyse (French power metal band)
- Operapop (Operatic pop duo)
- Operatica
- Operatika (symphonic metal)
- Operating Tracks, The
- Operating Tracks, The feat. Rein
- Operation
- Operation Ivy
- Operation M.D, The
- Operation Mindcrime
- Operation Sodasteal (kaj strife & slaney(in)famous)
- Opération Zéro
- Operation, The
- 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)
- Ophanin
- Ophelia Ragtime Orchestra
- Ophelia's Eye (Melodic death metal band from Switzerland)
- Ophelias, The (psychedelic rock band from San Francisco)
- Ophelias, The (Cincinnati indie rock band)
- Ophidian (hardcore dj)
- Ophidian & Peacock, Dr.
- Ophidian & Playah, Tha
- Ophidian I
- 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 du Peuple
- Opium Jukebox
- Opium Moon
- Opium Owl (heavy psych rock band from Riga, Latvia)
- Opium Warlords
- Opiuo (Australian electronica / breakbeat artist)
- Opiuo feat. Gift of Gab & Syreneiscreamy
- 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 (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