The Orlando Chorale
- A community chamber chorus in Orlando, Florida. Rehearsals, performances, and audition information.
- http://www.theorlandochorale.org/

Orlando Singers
- One of Southern England's most exciting and ambitious chamber choirs. From Dorset.
- http://www.orlandosingers.co.uk/

Orlando Chamber Choir
- 35-40 voices baroque choir from London, England.
- http://www.rubyred.demon.co.uk/

Orpheus Chamber Singers
- A professional 24-voice choir specializing in the performance of choral music of the last five centuries.
- http://www.orpheuschambersingers.org/

Ohlone Chamber Singers
- A 46 voice choir performing a wide range of music repertoire, from Renaissance through significant 20th century works. California.
- http://www.chambersingers.org/