| Holyhead to Oakley (California) | 5,097.52 mi (8,203.67 km) |
| Holyhead to Oakton (Virginia) | 3,458.91 mi (5,566.58 km) |
| Holyhead to Oakville (Missouri) | 3,989.28 mi (6,420.13 km) |
| Holyhead to Oatfield (Oregon) | 4,699.18 mi (7,562.60 km) |
| Holyhead to Ocala (Florida) | 4,128.74 mi (6,644.57 km) |
| Holyhead to Ocean Acres (New Jersey) | 3,298.72 mi (5,308.77 km) |
| Holyhead to Ocean City (New Jersey) | 3,333.18 mi (5,364.23 km) |
| Holyhead to Ocean Pines (Maryland) | 3,395.66 mi (5,464.78 km) |
| Holyhead to Ocean Pointe (Hawaii) | 7,040.70 mi (11,330.90 km) |
| Holyhead to Ocean Springs (Mississippi) | 4,333.41 mi (6,973.95 km) |
| Holyhead to Oceanside (California) | 5,231.68 mi (8,419.57 km) |
| Holyhead to Oceanside (New York) | 3,232.96 mi (5,202.95 km) |
| Holyhead to Ocoee (Florida) | 4,134.07 mi (6,653.15 km) |
| Holyhead to Oconomowoc (Wisconsin) | 3,697.88 mi (5,951.16 km) |
| Holyhead to Odenton (Maryland) | 3,426.41 mi (5,514.27 km) |
