The American trade deficit has grown continually since 2002, reaching a record high (6.2% of GDP) in 2005, even though the U.S. dollar's four-year decline has had a positive impact, estimated at nearly 1% of GDP, as expected from the J-curve mechanism (the depreciation of the exchange rate initially leads to a worsening of the trade balance, which is subsequently followed by an improvement as soon as competitiveness gains take ground). Improved non oil terms of trade, and cyclical divergence between the United States and the rest of the world, have also been favourable to the American trade balance. However, other factors have more than offset these positive effects. The United States' energy bill has increased by 1.4% of GDP. The low ratio of nominal exports to nominal imports, which spontaneously leads to a deterioration in the trade balance even if imports and exports grow at the same rate, explains a further deterioration of 1.7 % of GDP. The remaining source of deficit growth, accounting for 2.3 %, is due to unexplained factors such as "non-price competitiveness". The American trade balance is expected to remain at the same level as 2006. Based on this scenario, simulations suggest that in the short term, only a slowdown of the American economy (- 1% growth) could lead to a significant reduction in its trade deficit (by - 0.4% in 2007). Conversely, the cumulative effects of past depreciation are expected to have no impact beyond 2006 while a further depreciation of the dollar (of 10%) will not produce positive effects before 2008. An increase in the world growth outside the United States (+ 1%) would only have a limited effect on America's trade balance (from 0.1 to 0.2% of GDP) in 2007.