About a third of world energy consumption takes place in buildings. Although policy efforts aimed at improving energy efficiency in buildings have been around at least since the 70s, these policies have mainly been applied to new constructions. Nevertheless, substantive gains in energy efficiency are possible in already existing buildings. In fact where public policy has failed to have an impact, voluntary Green Building certification systems have emerged offering a whole building approach to improvements in energy efficiency and environmental sustainability. However, as this thesis will explain, each certification system has adopted different forms of energy performance assessment. One of these, known as benchmarking, involves assessing the energy performance of one building in relation to other similar buildings. This is the method advocated by the American Green Building certification system: Leadership in Energy and Environmental Design (LEED). As LEED has grown in popularity and become an internationally used certification system, it has allowed projects outside the United States to either be benchmarked against similar buildings in the US or to use a local benchmark for their energy performance assessment. This thesis investigates the most coherent strategy for existing office buildings in Austria wishing to perform best in the energy performance assessment component of LEED for Existing Building (LEED EBOM) version 3. In the process, this thesis highlights the problems related with applying a national system of assessment abroad and therefore the need to adopt the system to local conditions. This thesis concludes, based on presently available data, that existing office buildings in Austria perform best when benchmarked against US buildings rather than if the local benchmark were to be used.