This specialist post-graduate thesis paper deals with the internal reporting system of the public postal operator. The central goal is to analyze the current state of the internal reporting system of the public postal operators and to the liberalization of the postal market and the regulatory requirements determine the direction of its further development. The initial part of specialist post-graduate thesis paper work shows development, the current situation and the most current trends in the market of postal services in the European Union and the Republic of Croatia, and discusses the process of liberalization of the postal market in the European Union and its impact on the development of the postal market in the Republic of Croatia. The central part of specialist post-graduate thesis paper work present the cost allocation model in the context of regulatory requirements. Croatian Post has chosen the model which are the main determinants of access to "top-down", "historical cost" (HCA) as a cost basis, "fully distributed costs" (FAC) as the standard cost and the ABC method as a technique for the distribution of the most important types of costs. Croatian Post has chosen the model of cost accounting that is recommended by the regulator for the allocation of costs for each particular service within the universal area, began the transformation of the accounting system of financial accounting to cost and management accounting. The final part of specialist post-graduate thesis paper work shows how financial reporting by the centers of responsibility and monitor the performance of managers at the centers of responsibility. Financial reporting by narrower organizational units, different in type and status, has a important information role in achieving the objectives of the centers of responsibility as well as the entire company.