O Horse Names
| Name | Title | Alternate Titles |
| O Aven-Jur 1994 | USA | |
| O'Bajan 1892 | BAB | |
| O'Bajan OA* 1881 | BAB | |
| O'Bajan* (Kiss) NFD | Unk M | |
| O-Henrietta 1969 | USA | AK BLUE STAR or Blue List |
| Oahir 1939 | ES | |
| Oaza 1901 | POL | |
| Obaid 1914 | USA | BLUE STAR |
| Obajan-Siglavy OA* 1845 | BAB | |
| Oban 1928 | Span | |
| Obayyan 1968 | USA | AK BLUE STAR |
| Obeja 1862 | WEIL | |
| Obejan 1832 | POL | |
| Obejan OA* NFD | POL | |
| Obejan Srebrny 1851 | POL | |
| Obejan Szaraki OA* NFD | POL | |
| Obejan-Maciuk 1857 | POL | |
| Obejan-Szarak OA* 1882 | POL | |
| Obejanek 1882 | POL | |
| Oberon 1959 | USA | AK BLUE STAR or Blue List |
| Obeya 1894 | SE | AK Asil SO BCFS |
| Obeya 1940 | SE | AK Asil SO BCFS |
| Obeya NFD | SE | Asil |
| Obeyan c.1880 | SE | AK Asil SO BCFS |
| Obeyan El Seifi NFD | DB | |
| Obeyran II 1905 | DA | BLUE STAR |
| Obeyran* 1889 | HAM | AK BLUE STAR |
| Obra 1933 | POL | |
| Obsession TF 2000 | SE | Asil |
| Odaliska 1874 | POL | |
| Odaliska 1941 | RS | |
| Odessa* 1973 | UK | |
| Odette Saand-Fa 1967 | USA | AK Sub-Dwarka |
| Odysseja* 1894 | POL | |
| Odysseus HF 1994 | SE | AK Asil |
| Oferta 1894 | POL | |
| Ofir* 1933 | POL | |
| Ofirka 1939 | POL | |
| Oh My Shai* 1990 | SE | AK Asil |
| Okafs Jurnadnik 1986 | USA | |
| Okht El Ful 1956 | SE | AK Asil |
| Okras 1918 | USA | Blue List |
| Olaya* 1976 | SE | AK Asil |
| Olivia 1961 | USA | AK BLUE STAR or Blue List |
| Olnatar 1943 | ES | |
| Olympic Star 1952 | USA | |
| Om Dalal 1899 | SE | Asil BCFS |
| Om El Arab* 1967 | SE | AK Asil |
| Om El Ezz* 1975 | SE | AK Asil |
| Om El Khail* 1984 | SE | AK Asil |
| Om El Kheir* 1973 | SE | AK Asil |
| Om El Saad 1945 | SE | AK Asil SO BCFS |
| Om El Saad* 1975 | SE | AK Asil |
| Om Habeeba 1974 | SE | AK Asil |
| Om Habeeba 1977 | SE | AK Asil |
| Om Khamsa 1974 | SE | AK Asil SO |
| Om Masafi Malik* 1984 | SE | Asil |
| Om Sabra 1970 | SE | AK Asil |
| Omagh 1965 | USA | AK SO Sub-Basilisk |
| Oman 1926 | USA | AK |
| Omar 1913 | USA | Blue List |
| Omar II 1933 | POL | |
| Omar Khayyam 1938 | USA | Sub-Skowronek |
| Omaya* 1982 | SE | Asil |
| Omayma* 1964 | SE | AK Asil Blue List |
| Ombre Rose AH* 1995 | SE | AK Asil |
| Omega 1894 | POL | |
| Omera 1972 | SE | AK Asil |
| Omnia 1977 | SE | Asil |
| Omnia* 1966 | SE | AK Asil SO Blue List |
| Onara* 1979 | SE | Asil |
| Onrust 1903 | USA | AK Blue List |
| Onshooda 1974 | SE | AK Asil |
| Opal 1933 | POL | |
| Ophir 1917 | USA | AK Blue List |
| Opieka 1848 | POL | |
| Ora 1978 | SE | AK Asil |
| Oran 1940 | SE | AK Asil SO |
| Orasha 1984 | SE | Asil |
| Orashaan* 1988 | SE | Asil |
| Orashan* 1983 | SE | Asil |
| Oraya 1986 | SE | Asil |
| Orayan* 1990 | SE | Asil |
| Orbit 1958 | USA | |
| Orfan Bey 1992 | SE | AK Asil |
| Oriental 1907 | Span | |
| Oriental 1924 (USA) | USA | AK Blue List |
| Orin RSI 1967 | ES | AK SO Sub-Basilisk |
| Orjent 1894 | POL | |
| Ormuz 1929 | USA | Blue List |
| Ornis 1945 | Span | |
| Ornis* 1909 | POL | |
| OS Shammari 1988 | SE | AK Asil |
| Osceola 1952 | USA | Sub-Basilisk |
| Osiria 1977 | SE | AK Asil |
| Osmanie NFD | POL | |
| Osolette 1915 | USA | Blue List |
| Ostrogska c.1820 | POL | |
| Ostrouska 1837 | POL | |
| Othello 1957 | SE | Asil SO Blue List |
| Othmanee 1934 | USA | AK Sub-Basilisk |
| Ourida 1932 | ES | Sub-Basilisk |
| Outlaw* 1915 | UK | |
| Oxford Decimus 1969 | Aus | |
| Oxford Sunset 1964 | Aus | |
| Ozora NFD | POL | |
| Ozorees 1974 | SE | AK Asil |