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- Mark O'Connor (born 1961)
- Jamie O'Hara (born 1950)
- The O'Kanes
- Jamie O'Neal (born 1968)
- The Oak Ridge Boys
- Old Dogs
- Steven Lee Olsen (born 1985)
- Troy Olsen (born 1973)
- One Flew South
- One Horse Blue
- One More Girl
- Roy Orbison (1936–1988)
- Robert Ellis Orrall (born 1955)
- Orrall & Wright
- K.T. Oslin (born 1941)
- Marie Osmond (born 1959)
- James Otto (born 1973)
- Paul Overstreet (born 1956)
- Jake Owen (born 1981)
- Randy Owen (born 1949)
- Buck Owens (1929–2006)
Read more about this topic: List Of Country Music Performers