The importance of the energy sector is reflected in a number of economic and non-economic indicators. As a member of the European Union, the Republic of Croatia has great potential for the development of its energy sector, especially companies operating in it. One possibility by which companies can realize their potential are integration processes. They represent one of the key ways for a company to grow through takeovers, mergers, acquisitions, strategic alliances and joint ventures. The aim of this paper is to successfully present the theoretical aspect of integration processes, factors that have impact on the success of the same, and based on these findings and through a case study analyze the process of take over of Petrokemija ltd. by Terra mineralna gnojiva llc. In order to present the aim of this paper better, the paper is divided into two theoretical chapters and one chapter that consits case study. In the first theorteical chapter, the author presents integration processes and factors have impact on them. In the second theoretical chapter, the author presents the characteristics of the energy sector of the Republic of Croatia, and integration processes that have occured in the Republic of Croatia and in the European Union. In the final chapter, the author presents a case study in which the success of the takeover of the Petrokemija ltd. by the Terra mineralna gnojiva llc. is being analyzed.