U.S. companies adversely affected by unfair imports may seek a number of relief measures, including antidumping (AD) duties. The Department of Commerce (Commerce) classifies China as a nonmarket economy (NME) and uses a special methodology that is commonly believed to produce AD duty rates that are higher than those applied to market economies. Commerce may stop applying its NME methodology if it finds that China warrants designation as a market economy. In light of increased concern about China's trade practices, the conference report on fiscal year 2004 appropriations requested that GAO review efforts by U.S. government agencies responsible for ensuring free and fair trade with that country. In this report, the last in a series, GAO (1) explains the NME methodology, (2) analyzes AD duties applied to China and compares them with duties applied to market economies, and (3) explains circumstances in which the United States would stop applying its NME methodology to China and evaluates the potential impact of such a step. Commerce agreed with our findings, commenting that our report provides timely and helpful information on the NME methodology and its application to China.