Similar to some other metro systems in the world, the fare payable by a passenger depends on the approximate distance travelled. However, taking any particular station as the origin, the other stations fall into fare "zones" depending on the distance from the origin. The fare to all stations in a "zone" is the same and increases with distance, especially if the journey involves a harbour crossing. Adult fares range from HK$3.80 to $26.00. Concessionary fares are usually half the adult fare, and range from HK$2.40 to $13.00. Fares for the Airport Express Line are significantly higher.