| Difficult Run to Oerlinghausen | 4,016.52 mi (6,463.97 km) |
| Difficult Run to Oestrich-Winkel | 4,045.93 mi (6,511.30 km) |
| Difficult Run to Offenburg | 4,088.00 mi (6,579.00 km) |
| Difficult Run to Oftersheim | 4,087.98 mi (6,578.96 km) |
| Difficult Run to Ohrdruf | 4,130.41 mi (6,647.26 km) |
| Difficult Run to Ohringen | 4,130.27 mi (6,647.03 km) |
| Difficult Run to Olbernhau | 4,237.01 mi (6,818.81 km) |
| Difficult Run to Olching | 4,235.33 mi (6,816.10 km) |
| Difficult Run to Oldenburg | 3,966.73 mi (6,383.83 km) |
| Difficult Run to Oldenburg in Holstein | 4,034.98 mi (6,493.68 km) |
| Difficult Run to Olfen | 3,973.23 mi (6,394.29 km) |
| Difficult Run to Olpe | 4,010.37 mi (6,454.07 km) |
| Difficult Run to Olsberg | 4,026.70 mi (6,480.35 km) |
| Difficult Run to Oranienburg | 4,167.94 mi (6,707.64 km) |
| Difficult Run to Ortenberg | 4,077.98 mi (6,562.88 km) |
