Businesses and institutions in the United States spend an estimated $175 billion per year for energy. Of that, the fraction under performance contracts and energy service agreements is currently growing, aided by cheaper monitoring technology and integration with energy management and conservation systems. To estimate the potential savings as well as to help verify energy savings retrofits, the American Society of Heating, Refrigeration and Air Conditioning Engineers has developed Standard 90.1 to provide guidance when conducting energy simulations of buildings before they are constructed. Although the potential accuracy afforded by todays energy simulation programs is high, there is little agreement on current methods when developing the base case building. In addition, there are no current standards to guide the analysis of newly constructed, energy efficient buildings. This paper presents an energy simulation of a newly constructed state office building and compares the energy savings a past study the uses ASHRAE Standard 90.1 and a simulation regression method. Overall, while the results show significant differences between the ASHRAE Standard 90.1 and the calibrated simulation regression method.