A method of producing oil and gas from a gathering manifold or a well. The method includes the steps of channeling field production into a sealed vessel through an inlet pipe, and permitting oil and gas components of the field production to separate naturally from water and other fluids within the vessel. The method further includes the steps of evacuating the separated oil and gas from the vessel via pipelines attached to the vessel at locations corresponding to the separated oil and gas, and pumping seawater into the vessel to pressurize the vessel and thereby aid in the production of oil and gas from the vessel.