| Band | Years | Genre | | Band | Years | Genre |
| O'Jays, The (4) | | | | onLoad (1) | | |
| O'Malley's March (1) | | | | Ooberman (6) | | |
| O-Town (122) | | | | OOIOO (3) | | Experimental |
| o.a.r. (10) | 1998 - | Alternative Rock | | Opal (2) | | |
| O.C. Supertones, The (23) | 1996 - | Ska | | Operation Ivy (4) | | |
| Oak Ridge Boys (2) | | | | Opeth (11) | 1990 - | Doom Metal |
| Oasis (83) | 1991 - | Alternative Rock | | Oppera (1) | | |
| Oblivians, The (1) | | | | Orange County Supertones, The (23) | 1996 - | Ska |
| Obscured By Clouds (6) | | | | Orange Juice (5) | | |
| Ocean Blue, The (7) | 1987 - | Pop | | Orange Peels, The (3) | | |
| Ocean Blvd. Band (1) | | | | Orb (8) | | |
| Ocean Colour Scene (7) | | | | Orbital (11) | 1987 - | Electronica |
| Ocean Diesel (1) | | | | Orchards and Vines (2) | | |
| OCS (4) | | Rock | | Orchestral Manoeuvres in the Dark (3) | | |
| Octane (3) | | | | Orgy (76) | | Alternative Rock |
| Odds, The (4) | | | | Original Dixieland Jazz Band (3) | | Dixieland |
| Odetta (5) | | | | Osborne Brothers, The (3) | | Bluegrass |
| of a revolution (10) | 1998 - | Alternative Rock | | Osker (2) | | |
| Off The Hook (1) | | | | Other Ones, The (4) | | |
| Off The Record (1) | | | | Otis, My Man (1) | | |
| OFFkey (2) | | | | Our Lady Peace (98) | 1992 - | Rock |
| Offspring (90) | | | | Ours (18) | | |
| Ohio Players, The (5) | | | | Out Of Body Experience (1) | | |
| Oi Polloi (2) | | | | Outfield, The (3) | | |
| Oingo Boingo (1) | | | | Outkast (20) | | Rap |
| Old 97s (6) | | | | Outlaws, The (2) | | |
| Old Blue Moses (1) | | | | Oval (6) | | I.D.M. |
| Oleander (2) | | | | Over the Rhine (4) | 1989 - | Folk-Rock |
| Olive (1) | | Dance | | OverExertion (1) | | |
| Olivia Tremor Control (13) | | | | Overkill (3) | | |
| Olsen Brothers (4) | | | | Owsley (3) | | |
| On Loan (1) | | | | Oyster Band (3) | | |
| One 4 Him (2) | | | | Oysterhead (4) | | Jam Rock |
| One Generation (1) | | Christian A Cappella | | Ozomatli (1) | | |
| One Less Reason (3) | | | | Ozric Tentacles (4) | | |
| One True Voice (7) | | Pop | |
