| Castel Gandolfo to Olympia Heights (Florida) | 5,202.02 mi (8,371.84 km) |
| Castel Gandolfo to Omaha (Nebraska) | 5,180.13 mi (8,336.61 km) |
| Castel Gandolfo to On Top of the World Designated Place (Florida) | 5,145.29 mi (8,280.55 km) |
| Castel Gandolfo to Onalaska (Wisconsin) | 4,875.32 mi (7,846.07 km) |
| Castel Gandolfo to Oneida (New York) | 4,277.87 mi (6,884.57 km) |
| Castel Gandolfo to Oneonta (New York) | 4,275.29 mi (6,880.42 km) |
| Castel Gandolfo to Ontario (California) | 6,324.60 mi (10,178.46 km) |
| Castel Gandolfo to Ontario (Oregon) | 5,739.83 mi (9,237.36 km) |
| Castel Gandolfo to Opa-locka (Florida) | 5,190.27 mi (8,352.93 km) |
| Castel Gandolfo to Opelika (Alabama) | 5,129.50 mi (8,255.13 km) |
| Castel Gandolfo to Opelousas (Louisiana) | 5,523.07 mi (8,888.52 km) |
| Castel Gandolfo to Orange (California) | 6,345.01 mi (10,211.30 km) |
| Castel Gandolfo to Orange (Texas) | 5,615.08 mi (9,036.59 km) |
| Castel Gandolfo to Orange City (Florida) | 5,106.15 mi (8,217.55 km) |
| Castel Gandolfo to Orangeburg (South Carolina) | 4,890.23 mi (7,870.07 km) |
