In spite of the recent explosive gr owth in the use of office and networ k equi pment, there has been no recent st udy that est imates in detail how much electricit y is consum ed by that equipment in the Unit ed States. In this study, we examined energy use by offi ce equipment and network equipm ent at the end of 1999. We classified office equipment into 11 types; for each type we estimated annual energy consumpt ion for resi dential, com mercial, and industrial use by combi ning estimat es of stock, power requirem ents, usage, and saturat ion of power management. We al so classified net work equipment int o six types and estimated the annual energy consumption for each t ype. We found that total direct power use by office and networ k equi pment is about 74 TWh per year, which is about 2% of total electr icity use in the U.S. When el ectricity used by tel ecommunicati ons equipment and electr onics manufacturing is i ncluded, that figure rises to 3% of all el ectricity use (Koomey 2000). More than 70% of the 74 TWh/year is dedicated to office equipment for commercial use. We also found that power management cur rently saves 23 TWh/year, and compl ete saturati on and proper functioning of power managem ent would achieve additional savi ngs of 17 TWh/year . Furt hermor e, com plete saturation of night shut down for equipment not r equired to operat e at night would r educe power use by an additional 7 T Wh/year. Finally, we com pared our current estimate wit h our 1995 forecast for 1999. We found that the total differ ence between our current estim ate and the previous for ecast is less than 15% and ident ified the factors that led to inaccuracies in the previous forecast. We also conduct ed a sensitivi ty analysis of the uncer tainti es in our current forecast and ident ified the data set s that have the largest impact on our current estimate of energy use.