In the oil industry, xanthan gum is used in large quantities to thicken drilling mud. These fluids carry the solids cut by the drilling bit to the surface. Xanthan gum provides great "low end" rheology. When circulation stops, the solids remain suspended in the drilling fluid. The widespread use of horizontal drilling and the demand for good control of drilled solids has led to its expanded use. It has been added to concrete poured underwater, to increase its viscosity and prevent washout.