The development related to the corporate governance process in Turkey began with the Capital Markets Board (SPK) setting the "Local Corporate Governance Principles" in 2003 and the trading of the BIST Corporate Governance Index in 2007. These developments made the evaluation of financial performance of companies listed in the corporate governance index significant. Energy is one of the most important economic sectors supporting the development of all countries, regardless of their level of development. It has become a frequently used sector in urbanization and industrialization. Over the last quarter century, the interest of many companies in this sector, which has been constantly on the agenda due to its economic and environmental impacts, has increased. In this study, the differences between the financial performance indicators of energy companies listed in both BIST100 and BISTXKURY indices and only in BIST100 were examined. According to the findings of the study, it was determined that only the average of the energy companies listed in the BIST100 index is higher in terms of return on equity, current assets/total assets, earnings per share, and market value indicators. It was found that the averages of the energy companies listed in both BIST100 and BISTXKURY indices were higher in terms of leverage ratio and fixed assets/total assets indicators. In terms of return on assets, market value/book value, liquidity ratio, cash ratio, TobinQ, and total asset indicators, it was concluded that the averages of energy companies are similar regardless of whether they are included in the BISTXKURY index, and there is no difference between them. As a result of the study, it can be said that being included in the corporate governance index does not affect the financial performance indicators of companies.