Abstract
Energy markets play an important role in achieving sustainable development goals. The sector of energy has a huge impact on the environment, hence changes in it are the highest priority in the European Union. The process of shaping and developing the internal energy market plays an important role in improving the security of supply of energy resources for the entire union. It requires a number of political negotiations, strategic decisions regarding energy liberalization, in particular, the electricity and gas sectors, as well as the adoption of sectoral legislation. The aim of the conducted research is to estimate the level of development of energy markets in the EU countries and to indicate the position of Poland in comparison to other countries. The research was performed in several stages. The first phase consisted of selecting appropriate diagnostic variables that comprehensively describe energy markets in countries belonging to the European Union. The next stage was collecting data, subjecting them to standardization, and then, based on the agglomeration algorithm, the process of dividing into groups of similar countries was carried out. The research results can be used as guidelines for legal regulations being prepared in the energy sectors of all member states, which can be used for selected clusters comprising similar countries in terms of the development of energy markets.