[Excerpt] The United States is in the process of considering a number of trade agreements. In addition, the 111th Congress may address the issue of trade promotion authority (TPA), which expired on July 1, 2007. These agreements range from bilateral trade agreements with countries that account for meager shares of U.S. trade to multilateral negotiations that could affect large numbers of U.S. workers and businesses. During this process, Congress likely will be presented with an array of data estimating the impact of trade agreements on the economy, or on a particular segment of the economy. An important policy tool that can assist Congress in assessing the value and the impact of trade agreements is represented by sophisticated models of the economy that are capable of simulating changes in economic conditions. These models are particularly helpful in estimating the effects of trade liberalization in such sectors as agriculture and manufacturing where the barriers to trade are identifiable and subject to some quantifiable estimation. Barriers to trade in services, however, are proving to be more difficult to identify and, therefore, to quantify in an economic model. In addition, the models are highly sensitive to the assumptions that are used to establish the parameters of the model and they are hampered by a serious lack of comprehensive data in the services sector. Nevertheless, the models do provide insight into the magnitude of the economic effects that may occur across economic sectors as a result of trade liberalization. These insights are especially helpful in identifying sectors expected to experience the greatest adjustment costs and, therefore, where opposition to trade agreements is likely to occur. This report examines the major features of economic models being used to estimate the effects of trade agreements. It assesses the strengths and weaknesses of the models as an aid in helping Congress evaluate the economic impact of trade agreements on the U.S. economy. In addition, this report identifies and assesses some of the assumptions used in the economic models and how these assumptions affect the data generated by the models. Finally, this report evaluates the implications for Congress of various options it may consider as it assesses trade agreements.