| Artist | Year at the Gathering |
| Odd Squad Family | 2019, 2022 |
| Odd Fellaz | 2011 |
| Ol Dirty Bastard | 2004 |
| One Eyed Doll | 2016 |
| Onyx | 2009, 2012, 2013, 2016, 2022 |
| Open Mind Productions | 2011 |
| Open Minded | 2018, 2021 |
| Optimus The Wicked | 2011 |
| Optymus Music | 2017 |
| Organ Grinders | 2001 |
| Origix & DC | 2012, 2013 |
| OS7 | 2007, 2009, 2010, 2011, 2012 |
| Osirus Of Blind Insanity | 2013 |
| Ouija Macc | 2018, 2019, 2021, 2022, 2023, 2024 |
Our Inner Circle |
2024 |
| OushaBoo | 2010, 2011 |
| O-Villianz | 2012 |
