The Differential Sticking Tester measures the “Stuck Pipe Tendency Coefficient” of drilling fluids, and also determines how effective lubricants or treatments might be with any given drilling fluid. By measuring the area of cake building during a test, the Bulk Sticking Coefficient is obtained and read directly at the conclusion of the test. This coefficient takes into account both the friction, or “stickiness” of the filter cake, as well as the amount of cake building that would occur to stick the pipe in the hole.