The objective of this work is to determine the extent of the conformity of the Croatian energy sector with the conditions for membership in the EU. According to a comparative analysis an identification is made of the state of affairs in the energy sector in the EU, in the Republic of Croatia and in the applicant countries, the level at which the conditions for membership are fulfilled and the necessary measures that have to be implemented during the reform. The main conclusion is that the legal system itself in the area of the Croatian energy system is already mainly harmonised with the EU system. However, concrete application of the rules departs from the way rules are applied in the EU. Since these rules obtain their final form only during application, and the manner of interpretation and application is much harder to change than the rules themselves, particular attention needs devoting to practice in the process of adjustment.