An efficient and reliable transportation system is important to the marketing of U.S. grain since transport costs often account for a significant portion of the grain price in destination markets. Changes in a mode's transportation rate may divert the grain flow and ultimately influence prices in origin and destination markets. The objective of this paper is to explore the impact of transport rates on grain prices using a multi-destination, inter-temporal approach, which can better capture the dynamic influence of transportation rates on grain prices. Corn prices at two major port areas and selected domestic markets are included in the analyses as are barge rates on the Upper Mississippi and Illinois Rivers, rail rates linking selected production regions and domestic markets, and ocean rates linking the export ports to foreign markets. A multivariate time-series analysis and graphical models are employed to analyze monthly prices and transport rate series extending from January 1990 to December 2002. Results show barge and ocean rates influence corn prices in contemporaneous time and, in the longer-run, perturbations in ocean freight rates have the greatest influence on corn prices while shocks in barge rates account for a more modest 12 percent of variation in these prices. The rail rate linking the north central U.S. to the Pacific Northwest port area initially has a modest impact on corn price, however, over an extended time horizon its influence increases to account for about 12 percent of the variation in these prices. Perturbations in all transport rates (barge, rail, and ocean) account for 40-65 percent of the variation in domestic and export corn prices.