Improvements in energy efficiency over the past three decades have played a key role in limiting global increases in energy use and CO2 emissions. For IEA countries, energy efficiency gains since 1990 have led to annual energy savings of more than 16 EJ in 2005 and 1.3 Gt of avoided CO2 emissions. However, the recent rate of efficiency improvement has been much lower than in the past. The good news is that a large potential remains for further energy and CO2 savings across all sectors. In industry alone, the application of proven technologies and best practices on a global scale could save between 1.9 Gt and 3.2 Gt of CO2 emissions per year. In public power generation, if all countries produced electricity at current best practice levels, CO2 savings would be between 1.8 Gt and 2.5 Gt.