A gas density control system for airships is provide. The system embodies a hybrid ballonet and low pressure gas storage tank combination for regulating the density and volume of the airship lift gas, wherein the ballonet is fluidly connected to the storage tank by a transfer hose. The base of the ballonet is also sealed along an exterior surface of the length curvilinear geometric shaped storage tank so that as the storage tank selectively rotates the ballonet either wraps or unwraps around the length, whereby the lift gas transfer to and from the storage tank to the ballonet, respectively. A transfer hose reel is provided to rotate with the storage tank so that as the ballonet wraps about the storage tank the transfer hose winds about the transfer hose reel, and vice versa. Thereby the system precisely adjusts the ballonet's volume, which in turn controls its lifting force.