- Oak Field Trio
- Oak Ridge Boys SEE: Oak Ridge Quartet; Various Artists (Artistic); Various Artists (Festival)
- Oak Ridge Quartet
- Oaks, Bob
- O'Brien, Curly
- O'Day, Molly
- O'Dell, Mac
- O'Dell, Rudolph
- Odell, Wallace
- Oglesby Trio
- Olabelle, Alex, & Decon SEE: Campbell, Alex
- Old Country Church In The City
- Old Country Church Quartet
- Old Fashion Trio
- Old Fashioned Revival Hour Quartet
- Old Fashions
- Old Hickory Singers
- Old Kentucky Ike
- Old North Canton Quartet
- Olivarez Brothers
- Oliver, Tammy
- Ollen & Dennis
- Ollis, Rose
- Olsen, Bill SEE: Various Artists (Rubytone Sacred)
- Olshevski, David
- Olson Brothers Quartet
- O'Neal, Peggy
- O'Neal Family
- Ooten, Leon
- Ooten Family
- Oral & Joann
| - Orange Juice Quartet SEE: Various Artists (BRC)
- Original Carter Family SEE: Carter Family [Virginia]
- Original Friendly Four
- Original Gospel Trio
- Original Radioaires Quartet SEE: Radioaires
- Original Stamps Quartet SEE: Stamps Quartet
- Orr, Gayle
- Orrell, Lloyd SEE: Various Artists (Skylite)
- Orrell Quartet
- Osborne, Jimmie
- Osborne, L.C.
- Osborne, Lou & Sonny
- Osborne, Pearl SEE: Various Artists (Big 6); Various Artists (Big 6); Various Artists (Oak)
- Osborne, Sonny
- Osborne Brothers
- Ott, Doy
- Ott, Lonnie
- Our Lady Of Mt. Carmel Choir
- Outstanding Rebels Quartet SEE: Rebels Quartet
- Overholt, Milly SEE: Overholt, Ray
- Overholt, Ray
- Overholt Family SEE: Overholt, Ray
- Owen & Mack
- Owen, Eddie & Joan SEE: Lee, Gary
- Owen, H.B.
- Owens, Buck
- Owens, Darrell & Barbara
- Owens, Jay & Elizabeth
- Owens Family
- Owston, Chuck
- Ozark Mountain Trio
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