| City | Region |
|---|
| ›Ojuel | Castilla y León› |
| ›Oliva | Valencia› |
| ›Olivares | Andalucía› |
| ›Olivenza | Extremadura› |
| ›Olot | Cataluña› |
| ›Olvera | Andalucía› |
| ›Omenaca | Castilla y León› |
| ›Onda | Valencia› |
| ›Onteniente | Valencia› |
| ›Orce | Andalucía› |
| ›Orient | Balearic Islands (Mallorca)› |
| ›Orihuela | Valencia› |
| ›Ortigosa del Monte | Castilla y León› |
| ›Ortigueira | Galicia› |
| ›Osona | Castille and León› |
| ›Osonilla | Castille and León› |
| ›Osuna | Andalucía› |
| ›Otero de Herreros | Castilla y León› |
| ›Oviedo | Asturias› |
