| Niagara Falls to Oerlinghausen | 3,883.00 mi (6,249.08 km) |
| Niagara Falls to Oestrich-Winkel | 3,923.44 mi (6,314.17 km) |
| Niagara Falls to Offenburg | 3,973.41 mi (6,394.59 km) |
| Niagara Falls to Oftersheim | 3,967.68 mi (6,385.37 km) |
| Niagara Falls to Ohrdruf | 3,999.25 mi (6,436.18 km) |
| Niagara Falls to Ohringen | 4,009.24 mi (6,452.25 km) |
| Niagara Falls to Olbernhau | 4,102.25 mi (6,601.94 km) |
| Niagara Falls to Olching | 4,115.94 mi (6,623.97 km) |
| Niagara Falls to Oldenburg | 3,827.90 mi (6,160.42 km) |
| Niagara Falls to Oldenburg in Holstein | 3,886.58 mi (6,254.85 km) |
| Niagara Falls to Olfen | 3,842.94 mi (6,184.61 km) |
| Niagara Falls to Olpe | 3,882.97 mi (6,249.04 km) |
| Niagara Falls to Olsberg | 3,896.58 mi (6,270.93 km) |
| Niagara Falls to Oranienburg | 4,023.47 mi (6,475.15 km) |
| Niagara Falls to Ortenberg | 3,951.94 mi (6,360.04 km) |
