Operas 3,079 Organ music 774 Orchestral music 703 Oratorios 420 Overtures 409 Outlines, syllabi, etc 347 Outlines and syllabi 256 Oral histories 127 Oratory 97 Outdoor books 96 Online-Publikation 89 Observations 85 Observers' manuals 77 Orchestral music, Arranged 77 Online resources 70 Ouvrages avant 1800 67 Outlines 32 Orchestral excerpts 24 Organ masses 23 Ouvrages illustrés 22 Ouvrages pour la jeunesse 22 Odes 20 Organa 16 Oral interpretation of poetry 15 Obituaries 14 Offertories (Music) 13 One-act plays 13 Optical disks 10 Ouvrages de vulgarisation 10 Original cast recordings 8 Officers' handbooks 7 Old-time music 7 Opera films 6 Outline 6 Ouvrages de controverse 6 Oral history 5 Occult fiction 3 Official gazettes 3 Online databases 3 Orders in council 3 Outline maps 3 Ouvrages apologétiques 3 Observer's manuals 2 Occasional sermons 2 Octavo format (Printing) 2 Open form music 2 Oregon authors 2 Oaths 1 Obras de divulgación 1 Observer's manual 1 Occasional verse, English 1 Occasional verse, Latin 1 Occult fiction, American 1 Odes, Latin 1 Office of Economic Opportunity 1 Old English language films 1 One-person shows (Performing arts) 1 Onlays (applied decoration) 1 Online Resources 1 Online resource 1 Open Access Journals 1 Open educational resources 1 Open world video games 1 Opera adaptations 1 Ordination sermons 1 Organ scores 1 Ornate types (Type evidence) 1 Oslo (2009) 1 Ottawa (1987) 1 Ottawa (2009) 1 Ouvrages de référence 1 Ouvrages illustres 1 Ouvrages illustrès 1 Ouvrages illustrés 1 Oversize books 1 Oxford (2000) 1