| Difficult Run to Oak Harbor (Washington) | 2,320.17 mi (3,733.95 km) |
| Difficult Run to Oak Hills (Oregon) | 2,340.17 mi (3,766.13 km) |
| Difficult Run to Oak Lawn (Illinois) | 581.22 mi (935.39 km) |
| Difficult Run to Oak Park (California) | 2,302.33 mi (3,705.25 km) |
| Difficult Run to Oak Park (Illinois) | 586.48 mi (943.84 km) |
| Difficult Run to Oak Park (Michigan) | 392.38 mi (631.47 km) |
| Difficult Run to Oak Ridge (Florida) | 757.37 mi (1,218.86 km) |
| Difficult Run to Oak Ridge (New Jersey) | 210.81 mi (339.26 km) |
| Difficult Run to Oak Ridge (Tennessee) | 431.63 mi (694.64 km) |
| Difficult Run to Oakdale (California) | 2,336.35 mi (3,759.99 km) |
| Difficult Run to Oakdale (Minnesota) | 903.93 mi (1,454.73 km) |
| Difficult Run to Oakland (California) | 2,407.75 mi (3,874.90 km) |
| Difficult Run to Oakland (New Jersey) | 220.68 mi (355.14 km) |
| Difficult Run to Oakland Park (Florida) | 894.04 mi (1,438.82 km) |
| Difficult Run to Oakleaf Plantation (Florida) | 654.94 mi (1,054.03 km) |
