| Merthyr Tudful to Oswego (Illinois) | 3,851.84 mi (6,198.94 km) |
| Merthyr Tudful to Oswego (New York) | 3,308.93 mi (5,325.21 km) |
| Merthyr Tudful to Otsego (Minnesota) | 3,884.55 mi (6,251.58 km) |
| Merthyr Tudful to Ottawa (Illinois) | 3,885.80 mi (6,253.59 km) |
| Merthyr Tudful to Ottawa (Kansas) | 4,263.59 mi (6,861.59 km) |
| Merthyr Tudful to Ottumwa (Iowa) | 4,038.75 mi (6,499.75 km) |
| Merthyr Tudful to Overland (Missouri) | 4,070.68 mi (6,551.13 km) |
| Merthyr Tudful to Overland Park (Kansas) | 4,227.61 mi (6,803.68 km) |
| Merthyr Tudful to Overlea (Maryland) | 3,485.07 mi (5,608.68 km) |
| Merthyr Tudful to Oviedo (Florida) | 4,185.15 mi (6,735.35 km) |
| Merthyr Tudful to Owasso (Oklahoma) | 4,399.90 mi (7,080.95 km) |
| Merthyr Tudful to Owatonna (Minnesota) | 3,924.74 mi (6,316.26 km) |
| Merthyr Tudful to Owensboro (Kentucky) | 3,987.37 mi (6,417.05 km) |
| Merthyr Tudful to Owings Mills (Maryland) | 3,494.22 mi (5,623.40 km) |
| Merthyr Tudful to Owosso (Michigan) | 3,631.64 mi (5,844.56 km) |
