How important is the new goods margin in international trade?

We propose a methodology for studying changes in bilateral trade due to countries exporting goods that they did not export previously or exported only in small quantities. Applying this methodology to country pairs that undergo trade liberalization and to pairs in which one of the countries undergoes significant structural transformation, we find large increases on this extensive?or new goods?margin. Looking at country pairs with no major trade policy change or structural change, however, we find little or no increases on the extensive margin. Studying time series on trade by commodity, we find that data from before 1988 and 1989, when most major trading countries moved to the Harmonized System, are not compatible with data from afterward.