This study uses cluster analysis to examine simulated energy consumption of 134 U.S. LEED NC office buildings to classify buildings into high, medium, and low energy use intensity clusters. The analysis uses energy simulation results from the LEED database, as a comparably large data set of energy end uses from sub-meter data does not yet exist. The difference between the low energy use cluster and other clusters is explained mostly by lower process loads and lower heating energy intensity, and partly by lower intensities of other HVAC related end-uses. Lighting energy use shows the least variation between clusters. The lower heating energy intensity in the low intensity cluster is largely explained by lower roof U-values, lower window-to-wall ratio, and smaller building size. Unregulated process loads are the most significant contributor to total building energy use, accounting for 36%, 33%, and 31% of the energy use in the high, medium, and low intensity clusters, respectively. This analysis provides a quantitative evaluation of the large difference in energy intensities in high-performance office buildings, showing that these buildings are dominated by internal loads, especially unregulated process loads. (C) 2014 Elsevier B.V. All rights reserved.