| Ostrow Mazowiecka to Navodari | 660.72 mi (1,063.32 km) |
| Ostrow Mazowiecka to Negresti-Oas | 347.22 mi (558.79 km) |
| Ostrow Mazowiecka to Nehoiu | 551.54 mi (887.62 km) |
| Ostrow Mazowiecka to Ocna Mures | 451.46 mi (726.55 km) |
| Ostrow Mazowiecka to Odobesti | 538.53 mi (866.68 km) |
| Ostrow Mazowiecka to Odorheiu Secuiesc | 473.23 mi (761.59 km) |
| Ostrow Mazowiecka to Oltenita | 639.63 mi (1,029.38 km) |
| Ostrow Mazowiecka to Onesti | 501.67 mi (807.36 km) |
| Ostrow Mazowiecka to Oradea | 395.75 mi (636.90 km) |
| Ostrow Mazowiecka to Orastie | 483.73 mi (778.49 km) |
| Ostrow Mazowiecka to Oravita | 536.23 mi (862.98 km) |
| Ostrow Mazowiecka to Orsova | 558.36 mi (898.60 km) |
| Ostrow Mazowiecka to Otelu Rosu | 503.51 mi (810.32 km) |
| Ostrow Mazowiecka to Otopeni | 600.67 mi (966.68 km) |
| Ostrow Mazowiecka to Ovidiu | 662.80 mi (1,066.67 km) |
