from the Kansas City Fed
International trade is a growing share of economic activity in the United States and a determinant of economic growth. Over the last three decades, exports and imports have more than doubled as a share of gross domestic product. Moreover, the contribution of net exports to economic growth has also increased from a small drag from 2002 to 2005 to a positive contributor from 2006 to the end of 2013. Energy net exports were a substantial part of this change, as their contribution to annual real GDP growth increased from -0.1 percentage point (a drag) to 0.2 percentage point in the same periods.
Over the last two decades, two new technologies – hydraulic fracturing and horizontal drilling – brought significant structural change to the energy sector. After declining or holding steady from 1975 to 2005, energy production—including crude oil, natural gas, and natural gas liquids—increased starting in 2006. Partly as a result, net energy imports as a share of energy consumption fell by about half from 2005 to 2013 after having risen five-fold from 1960 to 2005.
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Source: http://kansascityfed.org/publicat/econrev/pdf/14q4Hakkio-Nie.pdf