This paper uses the econometrics of endogenous structural breaks to examine changes in energy intensity for OECD countries over 1960-2009. Nearly all OECD countries currently have significant negatively trending energy-GDP ratios; but for several countries those negative trends are recent, and two countries have recent significant positive trends. For several countries, energy intensity had a significant positive trend followed by a break and then a significant negative trend. Those break-dates, however, appear to have little to do with level of development (GDP per capita). Instead, among the likely causes of break timing are the volatile energy prices of the 1970s and early 1980s and the increased concern for the environment in the late 1960s and early 1970s. These findings have implications for future modeling of energy consumption as well as for the role of energy price policy in developed and developing countries.