| Merthyr Tudful to Olivares | 999.02 mi (1,607.76 km) |
| Merthyr Tudful to Olivenza | 919.87 mi (1,480.38 km) |
| Merthyr Tudful to Olot | 715.60 mi (1,151.65 km) |
| Merthyr Tudful to Onate | 603.44 mi (971.15 km) |
| Merthyr Tudful to Onda | 827.43 mi (1,331.62 km) |
| Merthyr Tudful to Onteniente | 902.67 mi (1,452.71 km) |
| Merthyr Tudful to Orihuela | 950.96 mi (1,530.42 km) |
| Merthyr Tudful to Osuna | 1,006.03 mi (1,619.06 km) |
| Merthyr Tudful to Ourense | 683.05 mi (1,099.26 km) |
| Merthyr Tudful to Oviedo | 590.43 mi (950.21 km) |
| Merthyr Tudful to Paiporta | 862.66 mi (1,388.32 km) |
| Merthyr Tudful to Pajara | 1,708.68 mi (2,749.85 km) |
| Merthyr Tudful to Palafolls | 753.51 mi (1,212.66 km) |
| Merthyr Tudful to Palafrugell | 745.25 mi (1,199.37 km) |
| Merthyr Tudful to Palamos | 749.18 mi (1,205.69 km) |
