Ocean alliances are groups of carriers who have agreed to pool their fleet of vessels to extend their service offerings and geographic coverage.
Three ocean alliances exist as of May 2018:
Alliances are pragmatic arrangements, so their compositions change every few years.
For more details about each alliance, see "Guide to Ocean Alliances" on Flexport's blog.
Alliances allow carriers to offer more sailing options with fewer vessels. If every carrier bought and operated the number of vessels needed to offer weekly sailings across every port they serve, the supply of vessel capacity would exceed the demand and container rates would fall. Carriers in an ocean alliance share their vessels so they can extend their service offerings and geographic coverage without flooding the market with vessels.
The merging of new ocean alliances will likely cause blank sailings.