| Merthyr Tudful to Octeville | 164.75 mi (265.13 km) |
| Merthyr Tudful to Oignies | 289.98 mi (466.67 km) |
| Merthyr Tudful to Oissel | 256.89 mi (413.43 km) |
| Merthyr Tudful to Olivet | 356.53 mi (573.77 km) |
| Merthyr Tudful to Ollioules | 733.07 mi (1,179.77 km) |
| Merthyr Tudful to Olonne-sur-Mer | 366.98 mi (590.60 km) |
| Merthyr Tudful to Oloron-Sainte-Marie | 604.56 mi (972.95 km) |
| Merthyr Tudful to Onet Village | 579.09 mi (931.96 km) |
| Merthyr Tudful to Onnaing | 316.90 mi (510.00 km) |
| Merthyr Tudful to Orange | 646.98 mi (1,041.21 km) |
| Merthyr Tudful to Orchies | 300.21 mi (483.15 km) |
| Merthyr Tudful to Orleans | 354.71 mi (570.86 km) |
| Merthyr Tudful to Orly | 328.40 mi (528.52 km) |
| Merthyr Tudful to Ormesson-sur-Marne | 331.53 mi (533.55 km) |
| Merthyr Tudful to Orsay | 323.56 mi (520.72 km) |
