| Name | Language | Saint | Meaning | Origin of the name | Celebration |
|---|---|---|---|---|---|
| Obicio | Español | Saint Obicio | 6 of December | ||
| Océano | Español | Saint Océano of Nicomedia | 18 of September | ||
| Octaviano | Español | Saint Octaviano | el octavo hijo | Latín | 20 of November |
| Octavio | Español | Saint Octavio of Turín | 20 of November | ||
| Oderisio | Español | Blessed Oderisio | 2 of December | ||
| Odilón | Español | Saint Odilón of Cluny | 1 of January | ||
| Odón | Español | Saint Odo of Cluny | Rico | Germánico | 18 of November |
| Odorico | Español | Blessed Odoric of Pordenone Mattiuzzi | 14 of January | ||
| Oengo | Español | Saint Oengo Cúldeo | 11 of March | ||
| Olegario | Español | Saint Olegarius | 6 of March | ||
| Olimpio | Español | Saint Olimpio of Tracia | 12 of June | ||
| Oliver | Català | Saint Oliverio Plunkett | 1 of July | ||
| Onesiforo | Español | Saint Onesíforo of Éfeso | 6 of September | ||
| Onésimo | Español | Blessed Onesimus | 15 of February | ||
| Onofre | Español | Saint Onophrius of Egypt | el que abre lo bueno | Griego | 12 of June |
| Optaciano | Español | Saint Optaciano of Brescia | 14 of July | ||
| Orestes | Español | Saint Orestes of Capadocia | Habitante de los Montes | Griego | 9 of November |
| Oriol | Español | Saint Joseph Oriol | 23 of March | ||
| Oscar | Español | Saint Ansgar of Bremen | 3 of February | ||
| Oseas | Español | Saint Oseas profeta | 17 of October | ||
| Oskar | Español | Saint Ansgar of Bremen | 3 of February | ||
| Osmundo | Español | Saint Osmundo | 4 of December | ||
| Ostiano | Español | Saint Ostiano of Viviers | 30 of June | ||
| Osvaldo | Español | Saint Osvaldo | 28 of February | ||
| Ovidio | Español | Blessed Ovidio Beltrán | 6 of November |