| Gaithersburg to Orbetello | 4,407.60 mi (7,093.35 km) |
| Gaithersburg to Oria | 4,760.24 mi (7,660.87 km) |
| Gaithersburg to Oristano | 4,377.57 mi (7,045.01 km) |
| Gaithersburg to Orta Nova | 4,644.88 mi (7,475.21 km) |
| Gaithersburg to Orte | 4,458.43 mi (7,175.15 km) |
| Gaithersburg to Ortona | 4,550.18 mi (7,322.81 km) |
| Gaithersburg to Orvieto | 4,437.27 mi (7,141.10 km) |
| Gaithersburg to Orzinuovi | 4,252.18 mi (6,843.22 km) |
| Gaithersburg to Osimo | 4,469.81 mi (7,193.47 km) |
| Gaithersburg to Ospitaletto | 4,253.08 mi (6,844.68 km) |
| Gaithersburg to Ostuni | 4,749.05 mi (7,642.86 km) |
| Gaithersburg to Ottaviano | 4,608.68 mi (7,416.95 km) |
| Gaithersburg to Ovada | 4,221.44 mi (6,793.76 km) |
| Gaithersburg to Ozieri | 4,372.90 mi (7,037.50 km) |
| Gaithersburg to Paceco | 4,628.29 mi (7,448.52 km) |
