| Houghton Regis to Orbetello | 853.16 mi (1,373.02 km) |
| Houghton Regis to Oria | 1,166.58 mi (1,877.43 km) |
| Houghton Regis to Oristano | 936.04 mi (1,506.41 km) |
| Houghton Regis to Orta Nova | 1,057.33 mi (1,701.60 km) |
| Houghton Regis to Orte | 888.12 mi (1,429.29 km) |
| Houghton Regis to Ortona | 959.88 mi (1,544.78 km) |
| Houghton Regis to Orvieto | 865.44 mi (1,392.79 km) |
| Houghton Regis to Orzinuovi | 654.42 mi (1,053.18 km) |
| Houghton Regis to Osimo | 870.75 mi (1,401.34 km) |
| Houghton Regis to Ospitaletto | 651.27 mi (1,048.12 km) |
| Houghton Regis to Ostuni | 1,152.80 mi (1,855.25 km) |
| Houghton Regis to Ottaviano | 1,042.28 mi (1,677.39 km) |
| Houghton Regis to Ovada | 654.59 mi (1,053.45 km) |
| Houghton Regis to Ozieri | 903.20 mi (1,453.57 km) |
| Houghton Regis to Paceco | 1,151.09 mi (1,852.50 km) |
