| South Houston to Orbetello | 5,612.57 mi (9,032.55 km) |
| South Houston to Oria | 5,962.18 mi (9,595.20 km) |
| South Houston to Oristano | 5,589.31 mi (8,995.13 km) |
| South Houston to Orta Nova | 5,847.27 mi (9,410.26 km) |
| South Houston to Orte | 5,662.03 mi (9,112.16 km) |
| South Houston to Ortona | 5,751.60 mi (9,256.30 km) |
| South Houston to Orvieto | 5,640.54 mi (9,077.58 km) |
| South Houston to Orzinuovi | 5,450.43 mi (8,771.62 km) |
| South Houston to Osimo | 5,669.26 mi (9,123.79 km) |
| South Houston to Ospitaletto | 5,450.65 mi (8,771.97 km) |
| South Houston to Ostuni | 5,950.46 mi (9,576.34 km) |
| South Houston to Ottaviano | 5,813.73 mi (9,356.29 km) |
| South Houston to Ovada | 5,423.52 mi (8,728.32 km) |
| South Houston to Ozieri | 5,583.43 mi (8,985.67 km) |
| South Houston to Paceco | 5,840.04 mi (9,398.64 km) |
