| Gretna to Olympia Heights (Florida) | 659.90 mi (1,062.00 km) |
| Gretna to Omaha (Nebraska) | 853.23 mi (1,373.14 km) |
| Gretna to On Top of the World Designated Place (Florida) | 470.11 mi (756.57 km) |
| Gretna to Onalaska (Wisconsin) | 967.88 mi (1,557.65 km) |
| Gretna to Oneida (New York) | 1,207.39 mi (1,943.11 km) |
| Gretna to Oneonta (New York) | 1,200.40 mi (1,931.86 km) |
| Gretna to Ontario (California) | 1,634.90 mi (2,631.11 km) |
| Gretna to Ontario (Oregon) | 1,765.00 mi (2,840.49 km) |
| Gretna to Opa-locka (Florida) | 658.88 mi (1,060.36 km) |
| Gretna to Opelika (Alabama) | 335.07 mi (539.25 km) |
| Gretna to Opelousas (Louisiana) | 128.44 mi (206.70 km) |
| Gretna to Orange (California) | 1,646.65 mi (2,650.02 km) |
| Gretna to Orange (Texas) | 222.38 mi (357.89 km) |
| Gretna to Orange City (Florida) | 531.55 mi (855.45 km) |
| Gretna to Orangeburg (South Carolina) | 593.63 mi (955.35 km) |
