| Gary to Olympia Heights (Florida) | 1,166.95 mi (1,878.03 km) |
| Gary to Omaha (Nebraska) | 451.38 mi (726.43 km) |
| Gary to On Top of the World Designated Place (Florida) | 908.08 mi (1,461.41 km) |
| Gary to Onalaska (Wisconsin) | 252.10 mi (405.71 km) |
| Gary to Oneida (New York) | 605.08 mi (973.78 km) |
| Gary to Oneonta (New York) | 632.61 mi (1,018.08 km) |
| Gary to Ontario (California) | 1,721.88 mi (2,771.09 km) |
| Gary to Ontario (Oregon) | 1,503.07 mi (2,418.95 km) |
| Gary to Opa-locka (Florida) | 1,157.09 mi (1,862.16 km) |
| Gary to Opelika (Alabama) | 626.38 mi (1,008.06 km) |
| Gary to Opelousas (Louisiana) | 808.62 mi (1,301.35 km) |
| Gary to Orange (California) | 1,740.23 mi (2,800.63 km) |
| Gary to Orange (Texas) | 869.29 mi (1,398.98 km) |
| Gary to Orange City (Florida) | 938.21 mi (1,509.91 km) |
| Gary to Orangeburg (South Carolina) | 662.15 mi (1,065.63 km) |
