Source: World Bank. United Nations, Review of Maritime Transport.
The growth of maritime transportation is strongly correlated with the growth of international trade since maritime shipping and ports are the main physical support for international trade flows. From about 800 million tons of loaded cargo in 1955, maritime traffic exceeded 8 billion tons for the first time in 2007, representing 32,500 ton-miles. Yet, maritime shipping is subject to fluctuations as commercial opportunities change. Major fluctuations in the value of exports in the 1970s and 1980s were mainly linked with economic recessions associated with the first and second oil shocks (1973 and 1979). More recently, the development and rapid diffusion of containerized maritime transportation were linked to a growing trade of value-added commodities. For every $1,000 of exports, there is the equivalent of one ton of freight being shipped by maritime transportation. From the late 1990s, a growing disconnect took place between the volume and value of maritime trade, mainly the outcome of the increasing added value of goods manufactured in Pacific Asia, rising energy (oil) prices, and the fragmentation of production since parts could be traded several times.
The ratio between the value of exports and the volume of seaborne trade remained constant until the first oil shock in 1973, underlining little changes in the composition of maritime shipping. The first two significant changes in this ratio corresponded to the first and second oil shocks, implying that higher oil prices directly impacted the global value of exports. Afterward, the steady growth of the ratio was mainly attributed to the growth in the containerized trade of high-value merchandise, particularly at the beginning of the 21st century. By 2007, containerized cargo accounted for about 52% of the value of seaborne trade. The financial crisis of 2008-2009 represented the most significant setback in global trade since the Great Depression in the 1930s, but global trade and maritime shipping recovered afterward.