The aim was to study the Energy Return on Investment (EROI) for the Fljotsdalsstod hydroelectric power plant (690 MW) using real data and a previously proposed standard. Energy return on investment is the ratio between the output and input energy. In this study we calculate the EROI within three defined boundaries, which include different parameters. Results show that over the 100-year lifetime, the plant is expected to deliver an EROI of approximately 110. The largest energy-consuming factor was the own usage, followed by the indirect energy used in the production of the construction materials. Since this study uses a standardised methodology, it can be compared to future studies. To date, this has not been possible since no standard methodology has been used in past studies. (C) 2014 Elsevier Ltd. All rights reserved.