Gate-to-gate process energy consumption is an important metric for sustainability as it affects both costs and environmental impact. As only little process information is available in early phases of chemical process design, a detailed energy consumption calculation is substantially restrained. Therefore, a reliable estimation of energy consumption in early phases of process design is an important alternative. In this work, an index representing process energy consumption was evaluated and tested for 14 organic solvent case studies. By using simplified process models the indices were calculated and compared to literature values for gate-to-gate energy consumption. The predictability of the process energy consumption on the basis of this indicator, including possible modifications in its original definition, was evaluated with the Pearson's and Spearman's correlation coefficients. The results further validated the use of the El (energy index) in its original form as a proxy indicator of the process energy consumption for decision making in early stages of process design. For assessing the production of new classes of chemicals the El should be evaluated as shown in this paper in order to establish its practicability. In certain cases an adjustment of the indicator categories may be necessary. (C) 2010 Elsevier Ltd. All rights reserved.