| Sintra to Olympia Heights (Florida) | 4,140.47 mi (6,663.44 km) |
| Sintra to Omaha (Nebraska) | 4,382.42 mi (7,052.82 km) |
| Sintra to On Top of the World Designated Place (Florida) | 4,122.56 mi (6,634.62 km) |
| Sintra to Onalaska (Wisconsin) | 4,079.86 mi (6,565.89 km) |
| Sintra to Oneida (New York) | 3,380.62 mi (5,440.59 km) |
| Sintra to Oneonta (New York) | 3,366.01 mi (5,417.07 km) |
| Sintra to Ontario (California) | 5,626.98 mi (9,055.75 km) |
| Sintra to Ontario (Oregon) | 5,151.93 mi (8,291.23 km) |
| Sintra to Opa-locka (Florida) | 4,129.67 mi (6,646.06 km) |
| Sintra to Opelika (Alabama) | 4,159.26 mi (6,693.68 km) |
| Sintra to Opelousas (Louisiana) | 4,573.58 mi (7,360.46 km) |
| Sintra to Orange (California) | 5,647.02 mi (9,087.99 km) |
| Sintra to Orange (Texas) | 4,672.89 mi (7,520.29 km) |
| Sintra to Orange City (Florida) | 4,076.42 mi (6,560.36 km) |
| Sintra to Orangeburg (South Carolina) | 3,902.37 mi (6,280.26 km) |
