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The present study has examined the relationship between energy intensity and economic efficiency and specifically, the inverted U-shaped relationship between these two variables in selected countries (17 developed countries and 14 developing countries including Iran) during 1991- 2011. In order to calculate the economic efficiency, we have employed data envelop analysis window method. Then, In order to estimate the impact of energy consumption intensity on economic efficiency, method of generalized moments has been used. The results show that an increase in energy intensity to an extreme point would increase economic efficiency too. However, after that point, an increase in energy intensity would be followed by a decline in economic efficiency. So, an inverted U shape relationship between energy intensity and economic efficiency is verified for the selected countries during this period.