In Hungary, gas storage facilities are porous geological structures. In most cases, the basic material is sandstone, excluding one being of limestone. Having extracted the original gas from these reservoirs, the geological formations, which were to a considerable extent depleted, were subsequently transformed to function as underground gas storage sites. Refurbishment included the conversion of wells bored originally to extract gas and the installation and construction of injection and gas preparation technology equipment.
The first facility serving as an underground gas storage site in the Hungarian system was constructed near Őriszentpéter. From 1960, natural gas stored here contributed to meeting the peak demand of Budapest during the winter period. However, the continuous increase in the demand for natural gas made it necessary to establish further underground storage facilities. The programme started in 1977 with the conversion of the depleted working natural gas field in the area of Kardoskút, and was continued the following year by commissioning two further facilities in Hajdúszoboszló and Pusztaederics. Currently, Hungarian Gas Storage Ltd. owns and operates four underground natural gas storage facilities: Zsana, Pusztaederics, Kardoskút, and Hajdúszoboszló.