Awareness of the importance of environmental protection and concern for society and its sustainability are one of the pillars in achieving and promoting sustainable development and thus continuous social and economic progress. This has led many companies to introduce sustainable development guidelines and sustainability reporting in their operations. In sustainability reports, companies show how their business affects the dimensions of sustainability: Economic, Social and Environmental. The introduction of a legal requirement for sustainability reporting has led large companies in the European Union (EU) to disclose information about sustainable business practices, which are increasingly becoming an important part of corporate operations. However, the lack of a uniform system for measuring corporate sustainability in the world and in the European Union, as well as the lack of measurements for the period after the introduction of the EU Directive 2014/95 on sustainability reporting, are incentives for the research in this dissertation. The objective of this dissertation is to develop a measurement system to assess the extent of sustainability reporting and sustainability performance in the operations of energy companies. To this end, data on the sustainable operations of the largest EU energy companies that are leaders in the EU energy sector were collected by analyzing the content of the companies' sustainability reports from 2016 to 2019. These are companies that, according to the EU Sustainable Energy System Strategy and the European Green Plan, are obliged to comply with energy laws and regulations and pursue sustainable development goals, and play a key role in sustainable development by improving energy efficiency and mitigating climate change. The dissertation has developed a system for measuring sustainability in the operations of EU energy companies by combining subjective (AHP) and objective (DEA) methods in the construction of sustainable operations. The measures of sustainable operations consist of a composite index for sustainability reporting and two composite indices for sustainability performance. Based on the developed metrics, the level of sustainability in the energy companies' operations was determined and their sustainability in operations was compared over the study period. This also solves the problem of the lack of sustainability measurement in the EU energy companies' operations for the period following the obligation to implement the Directive and sets the stage for longitudinal comparisons within the sector and for longer periods.iv The analysis of the content of the sustainability report revealed that energy companies do not adequately report on their sustainable operations and that, according to the information in the report, they mostly achieve extremely low and low levels of sustainability in their operations. Based on the tested first hypothesis and the applied correlation analysis, a correlation was found between sustainability reporting and sustainability performance of energy companies. Testing the second hypothesis and using fixed effects panel regression analysis, it was found that sustainability reporting and sustainability performance did not affect the profitability of energy companies in the period studied. This resulted in recommendations for improving corporate sustainability reporting, recommendations for measuring corporate profitability and continuing longitudinal monitoring, and recommendations for research on corporate sustainability and profitability. The scientific contribution of the paper is a theoretical contribution based on the systematization of knowledge about sustainability reporting and sustainability measurement in the operations of energy companies. It is a methodological contribution based on the design of measures and implementation of systematic measurement of sustainability in the operations of energy companies, as well as a practical contribution reflected in the practical application of sustainability measurement in the operations of energy companies.