| Holyhead to Orbetello | 1,045.88 mi (1,683.18 km) |
| Holyhead to Oria | 1,363.90 mi (2,194.98 km) |
| Holyhead to Oristano | 1,114.84 mi (1,794.16 km) |
| Holyhead to Orta Nova | 1,254.11 mi (2,018.30 km) |
| Holyhead to Orte | 1,082.83 mi (1,742.65 km) |
| Holyhead to Ortona | 1,156.61 mi (1,861.38 km) |
| Holyhead to Orvieto | 1,060.17 mi (1,706.17 km) |
| Holyhead to Orzinuovi | 850.64 mi (1,368.98 km) |
| Holyhead to Osimo | 1,067.83 mi (1,718.51 km) |
| Holyhead to Ospitaletto | 847.89 mi (1,364.54 km) |
| Holyhead to Ostuni | 1,350.21 mi (2,172.95 km) |
| Holyhead to Ottaviano | 1,237.44 mi (1,991.47 km) |
| Holyhead to Ovada | 846.87 mi (1,362.90 km) |
| Holyhead to Ozieri | 1,085.36 mi (1,746.72 km) |
| Holyhead to Paceco | 1,338.07 mi (2,153.41 km) |
