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Online markets for transportation services, in the form of Internet sites that dynamically match shipments (shippers ’ demand) and transportation capacity (carriers ’ offer) through auction mechanisms are changing the traditional structure of transportation markets. A general framework for the study of carriers ’ strategies in a transportation auction marketplace is provided. The unique characteristics of these marketplaces and the sources of difficulty in analyzing the performance of these marketplaces under different carrier bidding strategies are discussed. A simulation framework is used to explore the complex engineering and economic processes and issues that arise in a transportation marketplace, which are difficult to explore using standard analytical or statistical tools. Some results and the overall simulation framework are also discussed