| Harpenden to Oerlinghausen | 384.47 mi (618.75 km) |
| Harpenden to Oestrich-Winkel | 384.69 mi (619.09 km) |
| Harpenden to Offenburg | 433.44 mi (697.56 km) |
| Harpenden to Oftersheim | 426.53 mi (686.43 km) |
| Harpenden to Ohrdruf | 483.02 mi (777.34 km) |
| Harpenden to Ohringen | 468.70 mi (754.29 km) |
| Harpenden to Olbernhau | 596.38 mi (959.78 km) |
| Harpenden to Olching | 574.41 mi (924.42 km) |
| Harpenden to Oldenburg | 371.68 mi (598.17 km) |
| Harpenden to Oldenburg in Holstein | 496.43 mi (798.92 km) |
| Harpenden to Olfen | 330.69 mi (532.19 km) |
| Harpenden to Olpe | 356.84 mi (574.27 km) |
| Harpenden to Olsberg | 380.48 mi (612.32 km) |
| Harpenden to Oranienburg | 577.12 mi (928.79 km) |
| Harpenden to Ortenberg | 420.27 mi (676.37 km) |
