| Potomac to Orbetello | 4,411.52 mi (7,099.65 km) |
| Potomac to Oria | 4,764.28 mi (7,667.37 km) |
| Potomac to Oristano | 4,381.01 mi (7,050.55 km) |
| Potomac to Orta Nova | 4,648.90 mi (7,481.69 km) |
| Potomac to Orte | 4,462.41 mi (7,181.55 km) |
| Potomac to Ortona | 4,554.25 mi (7,329.36 km) |
| Potomac to Orvieto | 4,441.27 mi (7,147.53 km) |
| Potomac to Orzinuovi | 4,256.40 mi (6,850.01 km) |
| Potomac to Osimo | 4,473.97 mi (7,200.17 km) |
| Potomac to Ospitaletto | 4,257.33 mi (6,851.51 km) |
| Potomac to Ostuni | 4,753.12 mi (7,649.40 km) |
| Potomac to Ottaviano | 4,612.58 mi (7,423.23 km) |
| Potomac to Ovada | 4,225.50 mi (6,800.29 km) |
| Potomac to Ozieri | 4,376.46 mi (7,043.23 km) |
| Potomac to Paceco | 4,631.73 mi (7,454.05 km) |
