Jamin action is a physical phenomenon due to alternating globules of liquid and bubbles of gas in channel of capillary dimensions. It is beautifully illustrated in the Jamin capillary tube. This tube is easily prepared by placing a vacuum in communication with one end of an ordinary capillary tube, and filling with globules and bubbles by means of a wet cloth applied with the finger at the other end of the tube.

When the globules are in equilibrium their menisci have equal radii of curvature. By applying a pressure at one end of the tube the globules become "distorted," in that their menisci assume unequal radii of curvature. In this condition they are able to offer a small resistance to the applied pressure. In doing this they retain some of the fluid within the tube, and prevent its escape from the open end.

A natural reservoir may be described as a huge bundle of capillary tubes radiating in all directions from the well. The globules and bubbles offer a resistance to any hydrostatic pressure tending to push the fluids toward the open well. If this hydrostatic pressure is of sufficient intensity, it overpowers the combined resistance of all globules located on the radiating lines, but if it is not of sufficient intensity, these globules and bubbles may be said to dictate the conditions of production from the well. These alternative conditions with respect to pressure and resistance determine volumetric and capillary controls, respectively. Particular emphasis is placed upon the effects of Jamin action with regard to the rate of production, volume produced from the well, and percentage of ecovery from the sands by natural flow; also the features accompanying the use of pumps or gas-lifts are discussed. The forced drive is given a brief review, and the paper concludes with a description of the method of discriminating in the field between volumetric and capillary controls.