| Oscar S S | Hipodromo Chile
11-May-25,
Stanafuera |
| Oscar S. Barrera Iii | Aqueduct
20-Feb-26,
Capt Jax Parrow |
| Oscar Silva | Club Hipico Santiago
20-May-25,
Manifestation |
| Oscar Sosa | San Isidro
09-Dec-24,
Que Buen Chef |
| Oscar Torelli | San Isidro
02-Sep-23,
Angiola Maja |
| Oscar V. Carrete | Sunland Park
28-Feb-26,
One Famous Molly |
| Oscar Vinardi | San Isidro
27-Mar-25,
Emprestado |
| Oscar Walton | San Isidro
24-Jul-23,
Margal |
| Oscar Zavatarelli | Palermo
10-Mar-23,
Cringer |
| Osman C C | Valparaiso Sporting Club
14-Nov-23,
Leonne |
| Osman Iturralde | Ruidoso Downs
06-Jul-24,
Running King |
| Ossie Bant | Terang
07-Dec-09,
ELQUILITA LAD |
| Osvaldo Alfonso Urbina Hernandez | Laurel Park
02-Feb-26,
El Boticario |
| Osvaldo Castiglioni | San Isidro
30-Jan-25,
Clobber |
| Osvaldo D Davila | Palermo
07-Nov-23,
Sonador Dubai |
| Osvaldo Davila | San Isidro
19-Mar-25,
Don Master |
| Osvaldo Fontan | San Isidro
13-Mar-25,
Hefestos |
| Osvaldo Gini | San Isidro
10-Aug-24,
Silogismo |
| Osvaldo H H | Valparaiso Sporting Club
15-May-25,
Son Mis Lagrimas |
| Osvaldo Minervino | San Isidro
03-May-25,
Tarde Gris |
| Osvaldo N Uria | Palermo
31-Oct-23,
Diana Di |
| Osvaldo Ocasio | Mountaineer
10-Dec-25,
Ee Yah |
| Osvaldo Rojas | |
| Oswaldo Jose Urbaneja | |
| Oswaldo Neto | |
| Otabek Umarov | Gulfstream
29-Oct-23,
Kotyle |
| Otsu Tsuyoshi | Urawa
28-Feb-26,
Blue Glitter |
| Owen Burrows | Wolverhampton
09-Dec-25,
Sassicaia |
| Owen Cocking | York
11-May-23,
Ginger Luna |
| Owen Cullen | Bowen
06-Jun-15,
My King Oath |
| Owen Garber | Charles Town
11-Dec-25,
Tafaany |
| Owen Glue | Grafton
25-Jan-26,
Hardley Grey |
| Owen Lewis | Armidale
11-Dec-15,
Flying Kenya |