| Niagara Falls to Orbetello | 4,331.15 mi (6,970.31 km) |
| Niagara Falls to Oria | 4,677.86 mi (7,528.29 km) |
| Niagara Falls to Oristano | 4,318.68 mi (6,950.24 km) |
| Niagara Falls to Orta Nova | 4,563.39 mi (7,344.07 km) |
| Niagara Falls to Orte | 4,379.33 mi (7,047.86 km) |
| Niagara Falls to Ortona | 4,467.18 mi (7,189.23 km) |
| Niagara Falls to Orvieto | 4,357.60 mi (7,012.88 km) |
| Niagara Falls to Orzinuovi | 4,164.54 mi (6,702.18 km) |
| Niagara Falls to Osimo | 4,383.75 mi (7,054.97 km) |
| Niagara Falls to Ospitaletto | 4,164.43 mi (6,702.01 km) |
| Niagara Falls to Ostuni | 4,665.80 mi (7,508.89 km) |
| Niagara Falls to Ottaviano | 4,532.09 mi (7,293.70 km) |
| Niagara Falls to Ovada | 4,139.97 mi (6,662.64 km) |
| Niagara Falls to Ozieri | 4,309.91 mi (6,936.12 km) |
| Niagara Falls to Paceco | 4,568.85 mi (7,352.85 km) |
