| Greenock to Olympia Heights (Florida) | 4,212.52 mi (6,779.39 km) |
| Greenock to Omaha (Nebraska) | 3,974.37 mi (6,396.13 km) |
| Greenock to On Top of the World Designated Place (Florida) | 4,105.57 mi (6,607.28 km) |
| Greenock to Onalaska (Wisconsin) | 3,673.73 mi (5,912.30 km) |
| Greenock to Oneida (New York) | 3,150.30 mi (5,069.91 km) |
| Greenock to Oneonta (New York) | 3,156.94 mi (5,080.61 km) |
| Greenock to Ontario (California) | 5,079.73 mi (8,175.04 km) |
| Greenock to Ontario (Oregon) | 4,486.60 mi (7,220.49 km) |
| Greenock to Opa-locka (Florida) | 4,199.77 mi (6,758.87 km) |
| Greenock to Opelika (Alabama) | 4,034.82 mi (6,493.41 km) |
| Greenock to Opelousas (Louisiana) | 4,399.72 mi (7,080.67 km) |
| Greenock to Orange (California) | 5,100.09 mi (8,207.80 km) |
| Greenock to Orange (Texas) | 4,483.73 mi (7,215.86 km) |
| Greenock to Orange City (Florida) | 4,076.38 mi (6,560.30 km) |
| Greenock to Orangeburg (South Carolina) | 3,820.39 mi (6,148.33 km) |
