| Fort Collins to Orbetello | 5,459.98 mi (8,786.99 km) |
| Fort Collins to Oria | 5,781.86 mi (9,305.00 km) |
| Fort Collins to Oristano | 5,489.23 mi (8,834.06 km) |
| Fort Collins to Orta Nova | 5,672.95 mi (9,129.73 km) |
| Fort Collins to Orte | 5,500.21 mi (8,851.73 km) |
| Fort Collins to Ortona | 5,575.47 mi (8,972.85 km) |
| Fort Collins to Orvieto | 5,477.61 mi (8,815.37 km) |
| Fort Collins to Orzinuovi | 5,269.53 mi (8,480.49 km) |
| Fort Collins to Osimo | 5,486.38 mi (8,829.48 km) |
| Fort Collins to Ospitaletto | 5,266.77 mi (8,476.04 km) |
| Fort Collins to Ostuni | 5,767.83 mi (9,282.43 km) |
| Fort Collins to Ottaviano | 5,655.17 mi (9,101.12 km) |
| Fort Collins to Ovada | 5,261.60 mi (8,467.73 km) |
| Fort Collins to Ozieri | 5,471.41 mi (8,805.38 km) |
| Fort Collins to Paceco | 5,732.39 mi (9,225.39 km) |
