| Harpenden to Oberkirch | 436.44 mi (702.38 km) |
| Harpenden to Obernburg am Main | 435.90 mi (701.51 km) |
| Harpenden to Obernkirchen | 403.37 mi (649.16 km) |
| Harpenden to Oberschleissheim | 582.68 mi (937.73 km) |
| Harpenden to Oberstdorf | 564.21 mi (908.01 km) |
| Harpenden to Obertraubling | 584.71 mi (941.00 km) |
| Harpenden to Obertshausen | 417.47 mi (671.86 km) |
| Harpenden to Oberursel | 403.58 mi (649.50 km) |
| Harpenden to Ochsenfurt | 479.12 mi (771.06 km) |
| Harpenden to Ochsenhausen | 525.36 mi (845.48 km) |
| Harpenden to Ochtrup | 321.74 mi (517.79 km) |
| Harpenden to Odenthal | 326.16 mi (524.91 km) |
| Harpenden to Oelde | 362.88 mi (584.00 km) |
| Harpenden to Oelsnitz | 550.82 mi (886.45 km) |
| Harpenden to Oer-Erkenschwick | 325.45 mi (523.76 km) |
