The first three caverns, which represent the first phase of the development, are now fully available and with a current capacity of 60 million cubic meters.
Holford will have a capacity of up to 160 million cubic meters when all the eight caverns are commercially available at the end of 2012.
E.ON gas storage UK manager director Jo Vizor said creating and preparing the caverns for commercial operation has involved many complex engineering and solution mining techniques.
"It also involved our ability to draw on the expertise in UK and wider pan-European team has been crucial" added Vizor.
The Holford gas storage project will provide a vital resource throughout the year and will play a central role in helping to provide secure gas supplies to the UK.
Work on the facility started in 2005 with the creation of the underground gas storage caverns took about two and a half years.
