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. Refurbishment included the conversion of wells bored originally for the purpose of extracting gas and the installation and construction of injection and gas preparation technology equipment.
The first facility serving as underground gas storage for the Hungarian system was constructed near Őriszentpéter. From 1960, natural gas stored here was dedicated to assisting in 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 placing into operation two further facilities in Hajdúszoboszló, and Pusztaederics. Currently there are five underground natural gas storage facilities in operation: Zsana, Pusztaederics, Kardoskút, and Hajdúszoboszló.