According to the International Labor organization US multinationals account for a majority of exports and just under 40% of imports. At the same time, their share of both exports and imports decreased during the 80s and mid 90s (the article claims that an over 10% decrease is negligible, I beg to differ). Would be interesting to know what is happening right now!
Multinational Corporations
In 1995, trade associated with US multinational corporations – trade involving United States parents, their foreign affiliates, or both – accounted for 62% of all US exports of goods and for 39% of all US imports of goods. A substantial share of the remaining US exports and imports of goods is associated with affiliates of foreign companies in the United States. In 1995, 23% of US exports of goods and 34% of US imports of goods were associated with such affiliates. (BEA, United States Multinational’s Operations in 1995)The share in total US exports and imports accounted for by multinationals – both associated and intra-firm trade – has changed very little. Associated exports of MNCs declined from 77% in 1982 to 62% in 1995. Associated imports declined from 50% in 1982 to 39% in 1995.