The concentration of US imports is studied from transaction-level data. Concentration has fallen in the typical industry, while it is stable by industry-origin. Falling concentration is driven by the extensive margin: the number of exporting firms has grown, and the number of exported products has fallen relatively more for top firms. Instead, average revenue per product of top firms has increased. Top firms are converging at the industry level, but diverging within country. Finally, rising concentration from an origin is associated with falling prices, foreign entry and industry growth. These facts suggest that international competition coexists with national concentration.

美国进口的集中度是根据交易级别的数据来研究的。典型行业集中度有所下降，而按行业分类则保持稳定。集中度下降是由广泛边际驱动的：出口企业数量增加，而顶级企业的出口产品数量下降相对更多。相反，顶级公司每个产品的平均收入有所增加。顶级公司在行业层面趋同，但在国内却出现分歧。最后，原产地集中度的提高与价格下降、外国进入和行业增长有关。这些事实表明，国际竞争与国家集中并存。