| Niagara Falls to Olivares | 3,739.84 mi (6,018.69 km) |
| Niagara Falls to Olivenza | 3,651.21 mi (5,876.05 km) |
| Niagara Falls to Olot | 3,966.32 mi (6,383.17 km) |
| Niagara Falls to Onate | 3,720.51 mi (5,987.58 km) |
| Niagara Falls to Onda | 3,922.53 mi (6,312.70 km) |
| Niagara Falls to Onteniente | 3,947.87 mi (6,353.49 km) |
| Niagara Falls to Orihuela | 3,959.03 mi (6,371.44 km) |
| Niagara Falls to Osuna | 3,795.89 mi (6,108.90 km) |
| Niagara Falls to Ourense | 3,497.30 mi (5,628.36 km) |
| Niagara Falls to Oviedo | 3,556.97 mi (5,724.38 km) |
| Niagara Falls to Paiporta | 3,934.66 mi (6,332.22 km) |
| Niagara Falls to Pajara | 3,686.35 mi (5,932.60 km) |
| Niagara Falls to Palafolls | 3,996.18 mi (6,431.22 km) |
| Niagara Falls to Palafrugell | 4,005.38 mi (6,446.03 km) |
| Niagara Falls to Palamos | 4,006.46 mi (6,447.77 km) |
