Here you will find a document which helps to explain the story of gas. Please note, it is still branded as Transco material but Transco plc changed its name on 10th October 2005 to National Grid Gas plc. This and other educational items will be re-branded in due course and further material will be added at a later date.
All About Gas
You might find it interesting and useful to visit a website sponsored by National Grid in the US titled ngridenergyworld.