| Boulder to Oerlinghausen | 4,948.69 mi (7,964.14 km) |
| Boulder to Oestrich-Winkel | 5,019.10 mi (8,077.46 km) |
| Boulder to Offenburg | 5,088.68 mi (8,189.44 km) |
| Boulder to Oftersheim | 5,067.81 mi (8,155.86 km) |
| Boulder to Ohrdruf | 5,067.45 mi (8,155.28 km) |
| Boulder to Ohringen | 5,105.91 mi (8,217.17 km) |
| Boulder to Olbernhau | 5,155.82 mi (8,297.49 km) |
| Boulder to Olching | 5,213.45 mi (8,390.24 km) |
| Boulder to Oldenburg | 4,879.98 mi (7,853.57 km) |
| Boulder to Oldenburg in Holstein | 4,906.22 mi (7,895.79 km) |
| Boulder to Olfen | 4,919.61 mi (7,917.34 km) |
| Boulder to Olpe | 4,966.37 mi (7,992.60 km) |
| Boulder to Olsberg | 4,971.67 mi (8,001.13 km) |
| Boulder to Oranienburg | 5,049.97 mi (8,127.15 km) |
| Boulder to Ortenberg | 5,036.65 mi (8,105.71 km) |
