Mostyska (Ukrainian: Мостиська, Polish: Mościska) is a city in Lviv Oblast (province) of Ukraine. It is administrative center of the Mostyska Raion. Population is 9,150 (2001). There is a break of gauge where the railway systems of the two countries meet. To speed up though traffic, a track gauge changing facility of the SUW 2000 variable gauge axle system has been installed to allow fitted trains to pass through the break of gauge at walking pace.