O
- Orianthi
- Eva O (Christian Death)
- Karen O (Yeah Yeah Yeahs)
- Hazel O'Connor
- Sinéad O'Connor
- Kaori Okui (Princess Princess)
- Olivia
- Yoko Ono (The Plastic Ono Band)
- Dolores O'Riordan (The Cranberries)
- Joan Osborne
- Amanda Overmyer
Read more about this topic: List Of Female Rock Singers