Under market conditions, improvement of the management system has become a key element in the development of any oil company. The management technology of a large subsidiary cannot be purchased off-the-shelf, but can only be gradually improved. Therefore, the management of the subsidiary structure and the parent company needs to assess the changes carried out. The methodology for assessing the effectiveness of restructuring is considered on the example of changing the organizational structure of a subsidiary, because the problem of manageability is most significant for companies in the oil industry due to the scale of their activities. The proposed methodology can be used to justify the feasibility of investment decisions and increase the "transparency" of the company's management.