- O Come, O Come, My Dearest by Arne, Thomas Augustine
- O Death, Where Is Thy Sting by Händel, Georg Friedrich
- O del ben che acquisterò by Cesti, Antonio
- O del mio dolce ardor by Gluck, Christoph Willibald
- O diese Sonne! by Wagner, Richard
- Ô Dieu Brahma! by Bizet, Georges
- O dolcissima speranza by Scarlatti, Alessandro
- Ô don fatal et détesté by Verdi, Giuseppe
- O don fatale, o don crudel by Verdi, Giuseppe
- O du, mein holder Abendstern by Wagner, Richard
- O fatidica foresta by Verdi, Giuseppe
- O fior del giorno by Puccini, Giacomo
- O Gnade! Höchstes Heil! by Wagner, Richard
- O grandi occhi lucenti by Giordano, Umberto
- O Himmel, lass’ dich jetzt erflehen by Wagner, Richard
- O Isis und Osiris by Mozart, Wolfgang Amadeus
- Ô jours heureux by Meyerbeer, Giacomo
- O König, das kann ich dir nicht sagen by Wagner, Richard
- Ô légère hirondelle by Gounod, Charles
- O Lisbona, alfin ti miro by Donizetti, Gaetano
- O Lola ch’ai di latti la cammisa by Mascagni, Pietro
- O Lovely Peace by Händel, Georg Friedrich
- O luce di quest’anima by Donizetti, Gaetano
- Ô lumière de Troie! by Berlioz, Hector
- Ô ma chère compagne by Verdi, Giuseppe
- Ô ma lyre immortelle by Gounod, Charles
- Ô messager de Dieu by Massenet, Jules
- O mia cuna fiorita by Cilea, Francesco
- O mio babbino caro by Puccini, Giacomo
- O mio castel paterno… Nell’argilla maledetta by Verdi, Giuseppe
- O mio Fernando by Donizetti, Gaetano
- O mio piccolo tavolo ingombrato by Leoncavallo, Ruggiero
- Ô mon cher amant by Offenbach, Jacques
- O monumento! by Ponchielli, Amilcare
- Ô Nadir, tendre ami de mon jeune âge by Bizet, Georges
- O namenlose Freude! by Beethoven, Ludwig van
- Ô nature pleine de grâce by Massenet, Jules
- O nube! che lieve… Nella pace del mesto riposo by Donizetti, Gaetano
- Ô nuit, déesse de mystère by Piccinni, Niccolò
- Ô paradis sorti de l’onde by Meyerbeer, Giacomo
- O patria mia by Verdi, Giuseppe
- O Peace, the Fairest Child of Heaven by Arne, Thomas Augustine
- Ô petite étoile by Chabrier, Emmanuel
- Ô prêtres de Baal by Meyerbeer, Giacomo
- O puissante magie by Meyerbeer, Giacomo
- O qui coeli terraeque serenitas by Vivaldi, Antonio
- O rendetemi la speme… Qui la voce sua soave – Vien, diletto by Bellini, Vincenzo
- O Rest in the Lord by Mendelssohn, Felix
- O s’apre al riso, o parla, o tace by Händel, Georg Friedrich
- O Sachs! Mein Freund by Wagner, Richard
- O sancta justitia by Lortzing, Gustav Albert
- O scemami il diletto by Händel, Georg Friedrich
- O selige Wonne! by Mozart, Wolfgang Amadeus
- O solutaris Hostia – Rossini by Rossini, Gioachino
- Ô souverain, ô juge, ô père by Massenet, Jules
- O Süße! Traute! by Wagner, Richard
- O Thou That Tellest Good Tidings to Zion by Händel, Georg Friedrich
- Ô toi qui prolongeas mes jours by Gluck, Christoph Willibald
- O tu ch’innanzi morte by Monteverdi, Claudio
- O tu che in seno agli angeli by Verdi, Giuseppe
- O tu, Palermo terra adorata… Santo amor che in me favelli by Verdi, Giuseppe
- O vecchio cor, che batti by Verdi, Giuseppe
- Ô vin, dissipe la tristesse by Thomas, Ambroise
- O voi, che penate by Händel, Georg Friedrich
- O Walther, der du also sangest by Wagner, Richard
- O wär’ ich schon mit dir vereint by Beethoven, Ludwig van
- O Welt, so schön und blühend by Spohr, Louis (Ludwig)
- O wie ängstlich, o wie feurig by Mozart, Wolfgang Amadeus
- O Wolfram, der du also sangest by Wagner, Richard
- O wunden-wundervoller heiliger Speer by Wagner, Richard
- O zittre nicht, mein lieber Sohn by Mozart, Wolfgang Amadeus
- O, mein Leid ist unermessen by Weber, Carl Maria von
- O, musst du Hoffnung schwinden… Wie fass’ ich mich vor hoher Freude by Wagner, Richard
- O, wie will ich triumphieren by Mozart, Wolfgang Amadeus
- Obeissons quand leur voix appelle by Massenet, Jules
- Odi il voto, o grande Iddio by Verdi, Giuseppe
- Ogn’uno acclami by Händel, Georg Friedrich
- Ogni amatore by Piccinni, Niccolò
- Ogni momento dicon le donne by Mozart, Wolfgang Amadeus
- Ogni vento ch’al porto lo spinga by Händel, Georg Friedrich
- Oh dischiuso è il firmamento! by Verdi, Giuseppe
- Oh refrigerio by Verdi, Giuseppe
- Oh Sleep, Why Dost Thou Leave Me by Händel, Georg Friedrich
- Oh, chi torna l’ardente pensiero… Più che i vezzi e lo splendore by Verdi, Giuseppe
- Oh, de’ verd’anni miei by Verdi, Giuseppe
- Oh, Gentlemen, Listen, I Pray by Sullivan, Sir Arthur
- Oh! La pitoyable aventure! by Ravel, Maurice
- Oh! Nel fuggente nuvolo by Verdi, Giuseppe
- Ombra cara by Händel, Georg Friedrich
- Ombra cara, amorosa by Traetta, Tommaso
- Ombra mai fu by Händel, Georg Friedrich
- Ombre di mia prosapia by Ponchielli, Amilcare
- Ombre légère by Meyerbeer, Giacomo
- Ombre pallide by Händel, Georg Friedrich
- Ombre, piante, urne funeste by Händel, Georg Friedrich
- Or che il ciel a me ti rende by Mozart, Wolfgang Amadeus
- Or che il ciel a me ti rende by Mozart, Wolfgang Amadeus
- Or che siete speranze tradite by Händel, Georg Friedrich
- Or sai chi l’onore by Mozart, Wolfgang Amadeus
- Or son sola alfin respiro by Auber, Daniel
