4 The global cargo ship network data base represents the majority of cargo transported on ships. Our study is based on Sea-web’s arrival and departure records in the calendar year 2007 as well as Sea-Web’s comprehensive data on the ships’ physical characteristics. We restrict our study to cargo ships bigger than 10 , 000 GT (gross tonnage) which make up 93% of the world’s total capacity for ship cargo transport. From these we select all 16 , 363 ships for which AIS data are available, taken as representative of the global traffic and long- distance trade between the 951 ports equipped with AIS receivers (for details see Electronic Supplementary Material). For each ship we obtain a trajectory from the data base, i.e. a list of ports visited by the ship sorted by date. In 2007, there were 490 , 517 nonstop journeys linking 36 , 351 distinct pairs of arrival and departure ports. The complete set of trajectories, each path representing the shortest route at sea and colored by the number of journeys passing through it, is shown in Fig. 1a. Each trajectory can be interpreted as a small directed network where the nodes are ports linked together if the ship traveled directly between the ports. Larger networks can be defined by merging trajectories of different ships. In this article we aggregate trajectories in four different ways: the combined network of all available trajectories, and the subnetworks of container ships (3 100 ships), bulk dry carriers (5 498) and oil tankers (2 628). These three subnetworks combined cover 74% of the GCSN’s total gross tonnage. In all four networks, we assign a weight w$_{ij}$ to the link from port i to j equal to the sum of the available space on all ships that have traveled on the link during 2007 measured in GT. If a ship made the journey from i to j more than once, its capacity contributes multiple times to w$_{ij}$ . The directed network of the entire cargo fleet is noticeably asymmetric, with 59% of all linked pairs of ports being connected only in one direction. Still, the vast majority of ports (935 out of 951) belongs to one single strongly connected component, i.e. for any two ports in this component there are routes in both directions, though possibly visiting different intermediate ports. The routes are intriguingly short: only few steps in the network are needed to get from one port to another. The shortest path length l between two ports is the minimum number of nonstop connections one must take to travel between origin and destination. In the GCSN, the average over all pairs of ports is extremely small, 〈 l 〉 = 2 . 5. III. THE GLOBAL CARGO SHIP NETWORK