The concept of energy is one key component of science education curricula worldwide. While it is still being taught in many science classrooms from a mainly conceptual knowledge perspective, the need to frame the concept of energy as a socioscientific issue and implement it in the context of citizenship education and education for sustainable development, is getting more and more explicit. As we will be faced with limited fossil fuels and the consequences of global climate change in the future, students have to be supported in becoming literate citizens who are able to reach informed energy-related decisions. In this article, we focus on students' reasoning and decision-making processes about socioscientific energy-related issues. In more detail, we developed a paper-and-pencil measurement instrument to assess secondary school students' competencies in this domain. The functioning of the measurement instrument was analysed with a sample of 850 students from grades 6, 8, 10 and 12 using item response theory. Findings show that the measurement instrument functions in terms of reliability and validity. Concerning student ability, elaborate reasoning and decision-making was characterised by the use of trade-offs and the ability to weigh arguments and to reflect on the structure of reasoning and decision-making processes. The developed measurement instrument provides a complement for existing test instruments on conceptual knowledge about the concept of energy. It aims to contribute to a change in teaching about energy, especially in physics education in the sense of education for sustainable development.