Pendulum services involve a set of sequential port calls along a maritime range, commonly including a transoceanic service to ports in another range and structured as a continuous loop. They are almost exclusively used for container shipping with the purpose of servicing a market by balancing the number of port calls and the frequency of services. For instance, pendulum services between Asia and Europe have on average 8 to 10 containerships assigned involving 8 to 12 port calls. A service between Asia and the US West Coast would have 5 to 7 ships. Most transatlantic pendulum services have 6 to 8 containerships and involve 6 to 8 port calls.