| Potomac to Octeville | 3,645.28 mi (5,866.52 km) |
| Potomac to Oignies | 3,818.30 mi (6,144.96 km) |
| Potomac to Oissel | 3,767.36 mi (6,062.98 km) |
| Potomac to Olivet | 3,839.35 mi (6,178.84 km) |
| Potomac to Ollioules | 4,149.55 mi (6,678.05 km) |
| Potomac to Olonne-sur-Mer | 3,713.13 mi (5,975.71 km) |
| Potomac to Oloron-Sainte-Marie | 3,854.47 mi (6,203.18 km) |
| Potomac to Onet Village | 3,966.50 mi (6,383.46 km) |
| Potomac to Onnaing | 3,845.11 mi (6,188.11 km) |
| Potomac to Orange | 4,072.27 mi (6,553.69 km) |
| Potomac to Orchies | 3,828.42 mi (6,161.25 km) |
| Potomac to Orleans | 3,838.70 mi (6,177.79 km) |
| Potomac to Orly | 3,837.33 mi (6,175.59 km) |
| Potomac to Ormesson-sur-Marne | 3,842.39 mi (6,183.72 km) |
| Potomac to Orsay | 3,829.84 mi (6,163.54 km) |
