| Niagara Falls to Oberkirch | 3,977.03 mi (6,400.42 km) |
| Niagara Falls to Obernburg am Main | 3,973.02 mi (6,393.96 km) |
| Niagara Falls to Obernkirchen | 3,889.87 mi (6,260.14 km) |
| Niagara Falls to Oberschleissheim | 4,123.84 mi (6,636.68 km) |
| Niagara Falls to Oberstdorf | 4,104.10 mi (6,604.91 km) |
| Niagara Falls to Obertraubling | 4,120.67 mi (6,631.58 km) |
| Niagara Falls to Obertshausen | 3,953.34 mi (6,362.28 km) |
| Niagara Falls to Oberursel | 3,938.80 mi (6,338.88 km) |
| Niagara Falls to Ochsenfurt | 4,015.30 mi (6,462.00 km) |
| Niagara Falls to Ochsenhausen | 4,066.95 mi (6,545.13 km) |
| Niagara Falls to Ochtrup | 3,819.92 mi (6,147.57 km) |
| Niagara Falls to Odenthal | 3,855.04 mi (6,204.09 km) |
| Niagara Falls to Oelde | 3,868.03 mi (6,224.99 km) |
| Niagara Falls to Oelsnitz | 4,067.78 mi (6,546.45 km) |
| Niagara Falls to Oer-Erkenschwick | 3,840.34 mi (6,180.43 km) |
