| Potomac to Oerlinghausen | 4,005.22 mi (6,445.78 km) |
| Potomac to Oestrich-Winkel | 4,034.63 mi (6,493.11 km) |
| Potomac to Offenburg | 4,076.72 mi (6,560.84 km) |
| Potomac to Oftersheim | 4,076.68 mi (6,560.79 km) |
| Potomac to Ohrdruf | 4,119.11 mi (6,629.06 km) |
| Potomac to Ohringen | 4,118.97 mi (6,628.85 km) |
| Potomac to Olbernhau | 4,225.70 mi (6,800.61 km) |
| Potomac to Olching | 4,224.04 mi (6,797.93 km) |
| Potomac to Oldenburg | 3,955.42 mi (6,365.64 km) |
| Potomac to Oldenburg in Holstein | 4,023.70 mi (6,475.52 km) |
| Potomac to Olfen | 3,961.92 mi (6,376.09 km) |
| Potomac to Olpe | 3,999.07 mi (6,435.88 km) |
| Potomac to Olsberg | 4,015.39 mi (6,462.15 km) |
| Potomac to Oranienburg | 4,156.64 mi (6,689.46 km) |
| Potomac to Ortenberg | 4,066.68 mi (6,544.69 km) |
