| Merthyr Tudful to Odessa (Texas) | 4,875.43 mi (7,846.25 km) |
| Merthyr Tudful to Ogden (Utah) | 4,722.01 mi (7,599.34 km) |
| Merthyr Tudful to Oildale (California) | 5,272.05 mi (8,484.54 km) |
| Merthyr Tudful to Ojus (Florida) | 4,277.00 mi (6,883.17 km) |
| Merthyr Tudful to Okemos (Michigan) | 3,653.70 mi (5,880.06 km) |
| Merthyr Tudful to Oklahoma City (Oklahoma) | 4,505.71 mi (7,251.24 km) |
| Merthyr Tudful to Okmulgee (Oklahoma) | 4,440.46 mi (7,146.23 km) |
| Merthyr Tudful to Olathe (Kansas) | 4,232.84 mi (6,812.10 km) |
| Merthyr Tudful to Old Jamestown (Missouri) | 4,060.58 mi (6,534.88 km) |
| Merthyr Tudful to Oldsmar (Florida) | 4,277.84 mi (6,884.53 km) |
| Merthyr Tudful to Olean (New York) | 3,444.33 mi (5,543.12 km) |
| Merthyr Tudful to Olive Branch (Mississippi) | 4,230.96 mi (6,809.07 km) |
| Merthyr Tudful to Olivehurst (California) | 5,144.17 mi (8,278.74 km) |
| Merthyr Tudful to Olney (Maryland) | 3,517.46 mi (5,660.80 km) |
| Merthyr Tudful to Olympia (Washington) | 4,731.69 mi (7,614.93 km) |
