| Merthyr Tudful to Orangevale (California) | 5,156.20 mi (8,298.11 km) |
| Merthyr Tudful to Orchards (Washington) | 4,797.87 mi (7,721.42 km) |
| Merthyr Tudful to Orcutt (California) | 5,348.65 mi (8,607.82 km) |
| Merthyr Tudful to Oregon (Ohio) | 3,662.08 mi (5,893.55 km) |
| Merthyr Tudful to Oregon (Wisconsin) | 3,835.08 mi (6,171.96 km) |
| Merthyr Tudful to Oregon City (Oregon) | 4,819.19 mi (7,755.74 km) |
| Merthyr Tudful to Orem (Utah) | 4,762.99 mi (7,665.30 km) |
| Merthyr Tudful to Orinda (California) | 5,231.57 mi (8,419.39 km) |
| Merthyr Tudful to Orland Park (Illinois) | 3,837.00 mi (6,175.05 km) |
| Merthyr Tudful to Orlando (Florida) | 4,200.45 mi (6,759.97 km) |
| Merthyr Tudful to Ormond Beach (Florida) | 4,149.79 mi (6,678.44 km) |
| Merthyr Tudful to Oro Valley (Arizona) | 5,165.00 mi (8,312.27 km) |
| Merthyr Tudful to Oroville (California) | 5,120.45 mi (8,240.57 km) |
| Merthyr Tudful to Oshkosh (Wisconsin) | 3,754.02 mi (6,041.51 km) |
| Merthyr Tudful to Oskaloosa (Iowa) | 4,034.20 mi (6,492.41 km) |
