| O Leary | Jane | Apart/Together |  |
| O Leary | Jane | Piano Quintet (2005) |  |
| Ofenbauer | Christian | ZERSTÖRUNG DES ZIMMERS/DER ZEIT (2000), Konzertfassung für Streichquartett und Klavier |  |
| Ogenasjan | Edgar | Kvintet dlja dvuch skripok, alta, violncell i fortepiano in D (1955) |  |
| Oja | Eduard | piano Quintet (1935) |  |
| Oldberg | Arne | Piano Quintet in Cis minor, Opus 24 (1908) |  |
| Olesen | Thomas Agerfeldt | Bochum for pianoquintet (2003) |  |
| Olive | Vivienne | Ommaggio (1990) |  |
| Olofsson | Kent | Splinters - Silhouettes - Shadows (2010) for harpsichord & string quartet |  |
| Ordway | Scott | I. Piano Quintet No. 1: \"At the end of the long feast of goodness and time\" (2008); II. Mare Vitalis: Part II \"Townland\" (2016) |  |
| Orkin | Evgeni | Quintett für zwei Violinen, Bratsche, Cello und Klavier, Opus 61 |  |
| Ornstein | Leo | Quintette for piano and strings Opus 72 (publication date 2005) |  |
| Orrego-Salas | Juon | Encuentros for Piano Quintet |  |
| Otterstroem | Thorwald | Piano Quintet in C minor (1902) |  |