Great Lakes and seaway shipping generates $3.4 billion in business revenue annually in the United States. In 2002, ships moved 222 million tons of cargo through the seaway. Overseas shipments, mostly of inbound steel and outbound grain, accounted for 15.4 million tons, or 6.9%, of the total cargo moved. In 2004, seaway grain exports accounted for about 3.6% of U.S. overseas grain shipments, according to the U.S. Grains Council. In a typical year, seaway steel imports account for around 6% of the U.S. annual total. The toll revenue obtained from ocean vessels is about 25–30% of cargo revenue. The Port of Duluth shipped just over 2.5 million metric tons of grain, which is less than the port typically moved in the decade before the seaway opened Lake Superior to deep-draft oceangoing vessels in 1959.