Vessel Sharing Agreements (VSA) make it possible for two or more liner shipping companies to share a route in a similar way as code sharing agreements in the airline industry.
The collaboration makes it possible to deploy larger, and more energy efficient vessels on a route, as well as increasing the frequency of operation (and thereby making it more attractiveto migrate transportation to the more efficient transportation form).
Brueckner (2001) used simulation to conclude that collaboration agreements increase welfare.
Feeders take care of the end-transportation between main terminals and smaller ports. Feeders are essential for getting a sufficient volume on the main lines and make it possible to focus the big vessels on a backbone infrastructure.
Liner Shipping Network Design taking cooperation into account is essential for designing applicable networks. Maersk Line estimate that around 1/4 of their routes involve VSA, and about 1/2 of the feeder operations involve foreign feeders.
Although code sharing is well-studied for airline companies the nature of liner shipping is significantly different.
In liner shipping vessels are making round trips, while airline companies mainly fly in a star structure from the hubs. Agreeing on sharing a single leg in airline companies can be easy, while it can be difficult to agree on a whole route involving 10-20 port calls.