| South Portland to Orbetello | 3,938.68 mi (6,338.70 km) |
| South Portland to Oria | 4,290.04 mi (6,904.15 km) |
| South Portland to Oristano | 3,914.22 mi (6,299.33 km) |
| South Portland to Orta Nova | 4,174.83 mi (6,718.74 km) |
| South Portland to Orte | 3,988.86 mi (6,419.45 km) |
| South Portland to Ortona | 4,079.73 mi (6,565.69 km) |
| South Portland to Orvieto | 3,967.55 mi (6,385.15 km) |
| South Portland to Orzinuovi | 3,780.60 mi (6,084.29 km) |
| South Portland to Osimo | 3,998.66 mi (6,435.22 km) |
| South Portland to Ospitaletto | 3,781.32 mi (6,085.44 km) |
| South Portland to Ostuni | 4,278.65 mi (6,885.82 km) |
| South Portland to Ottaviano | 4,139.84 mi (6,662.43 km) |
| South Portland to Ovada | 3,751.16 mi (6,036.92 km) |
| South Portland to Ozieri | 3,908.08 mi (6,289.45 km) |
| South Portland to Paceco | 4,164.92 mi (6,702.80 km) |
