- O
- OO
- OO
- OO
- OOak
- OakOat
- OatObi
- ObiObs
- ObsOce
- OceOce
- OceOct
- OctOdd
- OddOde
- OdeODM
- OdmOer
- OerOff
- OffOff
- Offogo
- OGROh
- OhOhm
- OHMOja
- OjaOka
- OkaOkt
- OktOla
- OLAOld
- OldOle
- OleOli
- OliOli
- OliOll
- OllOLU
- OluOm
- OmOme
- OmeOmo
- OMOOna
- OOne
- OneOne
- OneOne
- oneOne
- ONFOnl
- Onl
- Oon
- OonOpe
- OpeOpi
- OpiOpu
- OpuOra
- OraOrb
- OrbOrc
- OrcOrd
- OrdOrg
- OrgOri
- OriOri
- OriOrm
- OrmOrp
- OrpOrr
- OrrOrt
- OrtOsb
- OsbOsc
- OscOsl
- Osl
- OstOte
- OTFOtr
- OTROtt
- OttOur
- ourOut
- OutOut
- OutOut
- OutOVE
- OVEove
- OveOVS
- OvtOWI
- OwiOxl
- OxlOzc
- OzcOzu
- Ozuozz
- Open Sky
- Open Skyz
- Open the Door for Three
- Open the Skies
- Open Trench
- Open University, The
- Open Up and Bleeds, The
- Open, The
- OpenBSD
- Openside
- Opensight (Metal)
- Opensouls
- Opera (Polish group)
- Opera (Italian hard trance project)
- Opera Alaska
- Opera Australia
- Opéra Bastille, Orchestre de l’, Chung, Myung-Whun
- Opera Chaotique
- Opéra de Nuit
- Opera Diabolicus (Doom/Black/Death Metal Swedish Band)
- Opera Familia
- Opera IX
- Opera Magna
- Opera Magna feat. Marta Barbé
- Opera Multi Steel
- OperaBabes
- Operación Triunfo (fake artist)
- Operación Triunfo 2009
- Operación Triunfo 2017
- Operación Triunfo 2018
- Operación Triunfo 2023
- Operación Triunfo 2025 (OT Series 13)
- Operación Triunfo, Academia
- Operaciya Plastilin
- Operadyse (French power metal band)
- Operapop (Operatic pop duo)
- Operatika (symphonic metal)
- Operating Tracks, The
- Operating Tracks, The feat. Anitchka, Emma
- Operating Tracks, The feat. Rein
- Operation
- Operation Cunt Destroyer (Scottish slam/brutal death metal/deathcore)
- Operation Ivy
- Operation M.D, The
- 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 (US indie rock band, Emily Arkin/Jen Godfrey/Paul Coleman)
- Operators, The (British indie rock band)
- Operators, The (ska, from Indianapolis, IN)
- Operazioni
- Operelly
- Operus
- Opeth (Swedish progressive metal/rock)
- OPFuture (German rapper)
- OPFuture & 4tune
- OPFuture & Niname
- OPFuture & Voodoo Beats
- OPFuture, Parker & Freakso
- OPFuture, Shwabadi & Charizma867
- Opgeduveld
- Opgekonkerd
- 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 & Minckz
- 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)
- Opia (Western Australian band)
- Opiate for the Masses
- Opick
