1978 – Beginning the transformation of Kardoskút depleted gas field into an underground storage site. The process continued in Pusztaederics and Hajdúszoboszló, by putting in operation these assets as well. The latest – in the 80ies - built storge site is Zsana. The operation of the underground storage sites was managed by MOL Földgáztároló Rt.
April 1, 2006 – After 16 months of approval procedure of the Hungarian and European authorities, E.ON Ruhrgas International AG (ERI) takes over 100% of the shares in MOL Földgázellátó Zrt and MOL Földgáztároló Zrt. The former natural gas storage company of Hungary has a new name and a new brand: E.ON Földgáz Storage Zrt.
2007 – Beginning the development of Zsana underground storage site.
November 2009 – Finishing the development of Zsana underground storage site, and through that the largest and most flexible underground storage site in Central-Eastern-Europe was putted in operation.
September 30, 2013 - MVM Hungarian Electricity Ltd. has paid in full the contractual purchase price for E.ON's Hungarian natural gas business interests. The company continues its operations as Hungarian Natural Gas Storage Ltd. owned by the Hungarian State, securing natural gas supplies for Hungary.