Underground storage of natural gas is a mature industry vital to a gas delivery system. It evolved as a sub-discipline of natural gas technology with certain additions and permits a steady supply of gas to serve a widely fluctuating demand. This book outlined the basic procedure for developing depleted oil reservoirs for underground gas storage and also analyzed the economics of running the storage systems. The book is essentially recommended for oil and gas operating companies; research institutions; government and investors who have interest in petroleum sector of the economy.