Abstract: A method for automatically regulating and measuring pressure as volatile substances in headspace gas are sampled and then quantitatively or qualitatively analyzed is disclosed. According to various embodiments, the method comprises vials that are automatically sampled by a headspace sampling instrument; the static pressure of the vials is automatically measured and recorded; the vials are automatically pressurized to a predetermined pressure that is greater than the static pressure; and the headspace gas is automatically allowed to flow into a sample loop of the headspace sampling instrument for subsequent qualitative or quantitative analysis. Multiple vials with varying static pressures may also be automatically measured, recorded and individually pressurized on a vial-by-vial basis as the headspace gas from each is automatically sampled and analyzed.