| South Portland to Smolyan | 4,542.19 mi (7,309.95 km) |
| South Portland to Sofia | 4,439.63 mi (7,144.90 km) |
| South Portland to Sopot | 4,499.30 mi (7,240.93 km) |
| South Portland to Sozopol | 4,627.43 mi (7,447.13 km) |
| South Portland to Sredets | 4,610.41 mi (7,419.74 km) |
| South Portland to Stamboliyski | 4,512.21 mi (7,261.70 km) |
| South Portland to Stara Zagora | 4,544.73 mi (7,314.04 km) |
| South Portland to Svilengrad | 4,595.34 mi (7,395.49 km) |
| South Portland to Svishtov | 4,482.85 mi (7,214.46 km) |
| South Portland to Targovishte | 4,547.32 mi (7,318.20 km) |
| South Portland to Teteven | 4,468.64 mi (7,191.58 km) |
| South Portland to Troyan | 4,488.19 mi (7,223.04 km) |
| South Portland to Tryavna | 4,520.36 mi (7,274.82 km) |
| South Portland to Tutrakan | 4,514.69 mi (7,265.69 km) |
| South Portland to Varna | 4,601.38 mi (7,405.21 km) |
