| Registered Name | Owner / Club | Status |
|---|---|---|
| OLS Inis Blath | Julie Finnegan Kilotteran | Approved |
| Olympic Diamond | Sue Perry Rock of Cashel | Approved |
| Olympic Gold Star | Sarah Devlin Castle Leslie | Approved |
| Olympic Sky | Patti Byrne Greenvalley | Approved |
| Omard Hannah | Shauna Wilson Benbulben | Approved |
| Omard Maria | Lucy Gilliland Mullaghmore | Approved |
| Omard Miss Molly | Orla O' Reilly Inishowen | Approved |
| Omeara Star | John Fenton Lismore | Approved |
| On A High | Sheanna Allman Moriarty Kerry | Approved |
| On Another Planet (GB) | John Wiseman Oakleaf | Approved |
| On Cloud Nine | Kathryn Taylor Clonshire | Approved |
| On The Bounce | Hazel Burke Ballycanew | Approved |
| On The Motorway (IRE) | Katherina Ivory Clonough | Approved |
| On Yellow Island (IRE) | Thomas Ryan Mullingar | Approved |
| Onatello | Caoilinn O'Rourke Corrib | Approved |