Tonnage of U.S. Waterborne Imports and Exports (monthly, not seasonally adjusted)
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SOURCES: April 1998–December 2005: U.S. Department of Transportation, Maritime Administration, U.S. Foreign Waterborne Transportation Statistics Data, September 2006. January 2006–present: U.S. Department of Commerce, U.S. Census Bureau, Foreign Trade Statistics, available at http://www.census.gov/foreign-trade/statistics/index.html as of August 2008.