The purpose of the article is to compare actual owners of European gas storage and transmission companies with preferred ones based on experts' assessments from the perspective of the Energy Union dimensions. Tasks of the research include explaining the topicality of the research, collecting data on owners of European gas storage and transmission companies, grouping companies in accordance with their ownership structures, obtaining expert assessments on preferred owners of the companies, comparing actual owners with preferred ones as well as drawing corresponding conclusions. Methods used area single linkage cluster analysis, structured expert interviews, analytic hierarchy process, monographic method, document analysis, case study method, literature review and others. The research covers gas storage and transmission companies in Europe, which are members of the Gas Infrastructure Europe Association. Companies are grouped into clusters according to the shares of the defined types of owners. Experts with sufficient knowledge on five dimensions of the Energy Union were interviewed in order to obtain assessments of preferred owners for the companies subject to research. Expert interview results were processed by using the analytic hierarchy process. At the final stage of the research, actual owners were compared to preferred ones derived from expert assessments and corresponding conclusions drawn. Six various clusters of gas storage companies and seven ones categorising transmission companies were identified while fifteen companies were defined as outliers. Apart from holdings by states of establishment, which constituted the most of observed cases, in many other instances both other European Union state as well as non-EU state holdings were revealed in the companies subject to research. Expert assessments processed by the analytic hierarchy process revealed the most and the least preferred clusters from the perspective of the five dimensions of the Energy Union. Copyright of European Integration Studies is the property of European Integration Studies: Research & Topicalities and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.