A simple concise breakdown from BLS.gov 
Excerpt: An analysis of the terms of trade index for the United States during the past 20 years indicates that the index has tended to vary by less than 10 percent. A spike in the import price index in 2008 (driven by sharply higher prices for fuels) was offset to some extent by a jump in the export price index (related to higher grain prices). (See chart 1.)Given the recent surge in market prices for petroleum as well as grains, the terms of trade for the United States will bear watching. Also see WSJ - "The Economy Is Worse Than You Thin"
Excerpt: An analysis of the terms of trade index for the United States during the past 20 years indicates that the index has tended to vary by less than 10 percent. A spike in the import price index in 2008 (driven by sharply higher prices for fuels) was offset to some extent by a jump in the export price index (related to higher grain prices). (See chart 1.)Given the recent surge in market prices for petroleum as well as grains, the terms of trade for the United States will bear watching. Also see WSJ - "The Economy Is Worse Than You Thin"