The European Network of Transmission System Operators plays a major role in creating uniform European markets for both electricity (ENTSOE) and gas (ENTSOG). Since its foundation in 2011 ACER (Agency for the Cooperation of Energy Regulators) has provided substantial assistance in accordance with its mandate to facilitate the cooperation of energy market regulators. The initial conceptualization of the framework guidelines and network codes for sub-themes started with the collaboration of the above organisations following regulations 714/2009/EC and 715/2009/EC of the European Parliament and the European Council. This article will first describe the most important changes (adopted 1 October 2015 for the most part) in connection with the above regulations and then elaborate as to their impact on the Hungarian transmission system, specificallywith regard to capacity sales in the gas market.