A self-regulating on-demand gas generator. Generation of gas produced from a reaction is selectively, variably, and spontaneously controlled. A variable volume liquid chamber in communication with the pressure pot allows the volume of liquid reactant in the pressure pot to be varied. The amount of product gas generated in the pressure pot depends on the degree of contact between the solid-like reactant and the liquid reactant. The pressure of the product gas regulates the level of liquid in the pressure pot and thereby regulates the degree of contact between the solid-like reactant and the liquid reactant. A sealed gas chamber sharing a flexible diaphragm with the liquid chamber controls the expandability of the liquid chamber. Manipulating the pressure in the sealed gas chamber or the volume of the liquid reactant affects the pressure at which contact by the reactants will be initiated or terminated and thereby provides the ability to control the reaction.