In the field of economic analysis, the study of the EU ETS policy has primarily focused on the impact of renewable energy consumption on economic growth, as well as the role of legal and fiscal instruments in the development of clean energy. This study aimed to evaluate the effectiveness of the EU ETS policy in altering the energy mix of selected European countries, providing both cognitive and applicational value. The evaluation of the effectiveness of this policy focused on the structure of the energy mix and the relationship between rising CO2 emission allowance prices and the decreasing share of coal in the energy mix. The goal was achieved through statistical analysis of secondary sources, primarily sourced from Bloomberg (2016–2024). The research findings indicated that changes in the structure of energy sources varied across the studied European countries, due to the adopted energy source utilization strategy, resource availability, and geopolitical situations. Additionally, different correlation values were noted between rising CO2 emission allowance prices and the expected reduction in fossil fuel use. Therefore, the EU ETS policy does not fulfill its assigned role—its implementation contributes to disparities in the economic situations of European economies and creates conditions for unequal competition.