I believe it could be the Initial Deposit which we pay for getting the Mahanagar Gas connection which was Rs 5K in old days but now might be much higher. This money remains with the company for a very long period, Say 20-30 years or even more as mostly connections are never disconnected by most of the customers. To me, this looks similar to a premium which Insurance companies get in advance and they invest it in various financial instruments and earn interest on your money. It is called as “Float” in case of insurance company, and Deposit looks similar to this “Float” for a CGD company. They can use for 30+ years without paying interest to customers as per my knowledge.
I might be wrong as well but I am trying to understand it by using similar analogy from insurance sector.