| Boulder to Orbetello | 5,493.33 mi (8,840.66 km) |
| Boulder to Oria | 5,815.86 mi (9,359.72 km) |
| Boulder to Oristano | 5,521.57 mi (8,886.10 km) |
| Boulder to Orta Nova | 5,706.80 mi (9,184.20 km) |
| Boulder to Orte | 5,533.75 mi (8,905.70 km) |
| Boulder to Ortona | 5,609.30 mi (9,027.30 km) |
| Boulder to Orvieto | 5,511.16 mi (8,869.36 km) |
| Boulder to Orzinuovi | 5,303.30 mi (8,534.84 km) |
| Boulder to Osimo | 5,520.29 mi (8,884.05 km) |
| Boulder to Ospitaletto | 5,300.59 mi (8,530.48 km) |
| Boulder to Ostuni | 5,801.87 mi (9,337.21 km) |
| Boulder to Ottaviano | 5,688.73 mi (9,155.12 km) |
| Boulder to Ovada | 5,295.02 mi (8,521.52 km) |
| Boulder to Ozieri | 5,503.98 mi (8,857.79 km) |
| Boulder to Paceco | 5,765.01 mi (9,277.89 km) |
