In accordance with the present invention, a method and system is described for controlling the delivery of vapor from a bubbler containing a supply of chemical fluid through which a carrier gas is bubbled and from which bubbler vapors are delivered in a vapor stream entrained with the carrier gas. In general, the present invention involves equilibrating the pressure within the head space to that of the chemical fluid fill line, thus maintaining a constant fluid level based on pressure and not relying on conventional level sensors and controllers.