This study examines how US discretionary practices in anti-dumping (AD) proceedings have developed and affected the extent of dumping margins of exporters in the past decade. Using detailed data on dumping margin calculations by the US Department of Commerce (DOC) from 2008 to 2020, we find that the DOC has endeavored to develop discretionary practices in a more nuanced way to inflate dumping margins for both ‘cooperative’ and ‘uncooperative’ exporters. Our statistical and case study show that although the practices known as targeted dumping and particular market situation are associated with smaller dumping margins than overall dumping margins, they critically increase the extent of dumping margins for cooperative exporters of market economies (ME), sometimes resulting in positive dumping determinations which would otherwise have been negative. We also empirically find that there has been an apparent change in the use of adverse facts available (AFA) that has led to much higher dumping margins for ‘uncooperative’ exporters of ME and non-market-economy (NME)-wide entities since the amendment of the Trade Preferences Extension Act (TPEA) of 2015.