Below is a list of Oil Pressure Gauge manufacturers from California. Oil pressure gages are instruments used to measure the pressure of oil in an enclosure. All objects exhibit forces of resistance against all other objects with which they come into contact. When a small amount of oil is placed in a cup, for example, it exerts force against the materials with which it comes into contact: air and the cup. If the oil were forced into a tank, as more oil was forced in, the force exerted against the tanks walls would increase. That force, or pressure, is an expression of quantity and concentration, and its measurement indicates both.