Abstract - Analysis of data center energy efficiency trends over the past decade, supported by detailed power usage data from over 300 data centers, shows that significant improvements have been made. However, Uptime Institute’s analysis also shows that very substantial energy reduction opportunities still remain untapped. While gains in mechanical and electrical efficiency have stalled over the past few years, it remains that over 65% of the power used by IT in data centers is used to process just 7% of the work, due to aging equipment inefficiencies. But if it is time for operators to pay more attention to IT energy efficiency, they need to do their analysis carefully: the slowdown in Moore’s law is creating new complications.