| Holyhead to Oswego (Illinois) | 3,758.36 mi (6,048.49 km) |
| Holyhead to Oswego (New York) | 3,223.10 mi (5,187.09 km) |
| Holyhead to Otsego (Minnesota) | 3,783.23 mi (6,088.53 km) |
| Holyhead to Ottawa (Illinois) | 3,792.30 mi (6,103.12 km) |
| Holyhead to Ottawa (Kansas) | 4,167.84 mi (6,707.49 km) |
| Holyhead to Ottumwa (Iowa) | 3,942.76 mi (6,345.25 km) |
| Holyhead to Overland (Missouri) | 3,978.97 mi (6,403.53 km) |
| Holyhead to Overland Park (Kansas) | 4,132.03 mi (6,649.87 km) |
| Holyhead to Overlea (Maryland) | 3,405.68 mi (5,480.91 km) |
| Holyhead to Oviedo (Florida) | 4,115.94 mi (6,623.96 km) |
| Holyhead to Owasso (Oklahoma) | 4,306.00 mi (6,929.84 km) |
| Holyhead to Owatonna (Minnesota) | 3,824.89 mi (6,155.57 km) |
| Holyhead to Owensboro (Kentucky) | 3,899.72 mi (6,276.00 km) |
| Holyhead to Owings Mills (Maryland) | 3,414.46 mi (5,495.05 km) |
| Holyhead to Owosso (Michigan) | 3,539.91 mi (5,696.93 km) |
