From the thesis abstract: "This research develops an attacker-defender model of maritime trading. The defender's problem is represented as a minimum cost, multi-commodity network flow model. System cost is measured in terms of total ton-n.m. in the network. Our network contains the 120 most important ports in the world (by volume of cargo), 35 waypoints at sea, and 416 arcs. Port supply and demand have been estimated from different sources. Interdictions represent manmade disruption of the seaways, such as those in the presence of piracy. An interdicted arc is assumed to incur a penalty equivalent to the additional distance that a ship would need to travel in order to avoid the threat, or a total blockade of the arc in the case of straits and canals. We analyze several scenarios with varying assumptions on the defended arcs and the number of simultaneous interdictions. The most disruptive, single interdiction occurs in the Strait of Gibraltar, increasing cost by almost 25%, followed by the Straits of Bab el Mandeb (20%) and Suez Canal (19%). For two simultaneous interdictions, cost increases to 33%, but decreases to 23%, 8% and 1.5% when we defend three, four or five select straits and canals, respectively."