O
| O.H. | Thrash Metal/Hardcore | Видин/София | 2001 |
| O.K. Girls! | Sleaze Rock/Glam Rock | София/Германия | 1989 |
| Obsidian Sea | Doom Metal | София | 2009 |
| Occultum | Black Metal | София | 2011 |
| Oceansoul | Alternative Rock | Бургас | 2023 |
| Oceanwide | Alternative Rock | София | 2015 |
| Odd Crew | Groove Metal/Metalcore | София | 2008 |
| Oddplay | Psychedelic Stoner Rock | Варна | 2019 |
| Odium | Death Metal | Плевен | 1992 |
| Off | Punk | Плевен | 1999 |
| Offroad | Heavy Metal | София | 2006 |
| Ogi 23 | Punk Rock/Ska | София | 2005 |
| OJ Band | Classic Rock/Country Rock | София | 2002 |
| Okupator | Punk/Thrash/Black Metal | Сандански | 2020 |
| Old Joe's Anger | Hardcore/Punk | Ловеч | 2004 |
| Ollie | Pop Punk | София | 2005 |
| Omerta | Hardcore Punk | София | 2005 |
| Omraz | Progressive Death Metal/Deathcore | Враца | 2022 |
| On Our Own | Metalcore/Hardcore | Варна | 2006 |
| On Wings | Doom Metal | София | 1994 |
| Once | AOR | Бургас | 2011 |
| One Day Less | Alternative Rock | София | 2020 |
| One Faith | Hardcore | Варна | 2001 |
| Ophan | Experimental Math Metal | София | 2006 |
| Ophidian Clasp | Metalcore/Deathcore | Перник | 2015 |
| Opiumortem | Raw Black Metal | София | 2022 |
| Oppressor | Thrash/Death Metal | София | 1992 |
| Order Of Splendour | Black/Death Metal | Плевен | 1998 |
| Orenda | Black Metal | Враца | 2004 |
| Ork | Black Metal | Дупница | 1997 |
| Orpheus | Raw Black Metal | Пловдив | 2025 |
| Out Of Muse | Pop Rock/Alternative | София | 2021 |
| Out Of This World | Raw Black Metal | Варна | 2006 |
| Out Of Tune | Hard Rock/AOR | Шумен | 2012 |
| Outer Space Experiment | Stoner Metal/Post Rock/Alternative | България/Италия/Франция | 2022 |
| Outrage | Hardcore | Варна | 1996 |
| Outsider | Thrash Metal | Ямбол | 1990 |
| Ovader | Black Metal | София | 2016 |
| Overdawn | Metalcore/Deathcore | Русе | 2002 |
| OverGame | Progressive Metal | София | 2008 |
| Overhook | Alternative Rock | София | 2021 |
| Ozone Friendly | Blues Rock | Горна Оряховица | 2012 |