While the bulk of global maritime trade takes place on open seas, the configuration of continental masses coupled with patterns of market demand, production, and resource extraction forces convergence of maritime trade at three major bottlenecks; the Panama Canal, the Suez Canal, and the Strait of Malacca. Their physical and operational characteristics dictate the volume and capacity of ships transiting through them. Capacity can be measured in deadweight tons (dwt), which is the mass a ship can carry, and in TEUs, which is the volume a containership can carry. The capacity of a passage in deadweight tons (dwt) does not relate effectively with the capacity in TEU. For instance, a 220,000 dwt containership would have a capacity of about 20,000 TEU and a draft of 16.5 meters, while a similar tanker would have a draft reaching 21 meters. The reason behind this lies in the cargo density, also known as the stowage factor, which is the ratio between cargo volume and cargo weight. For containers, the average cargo density is about 3 cubic meters per ton, while for oil and iron ore, this ratio is 1.1 and 0.44 cubic meters per ton respectively.
The capacity of a strategic passage is also a function of the number of transits it can handle. Panama can handle about 45 transits per day, while this figure is about 100 (78 before the expansion) per day for Suez. The capacity of the Strait of Malacca is difficult to assess, but about 210 commercial ships are transiting each day. By handling about 30% of the global maritime trade, Malacca is the most important passage in the global economy, followed by Suez (15%) and Panama (5%).