Abstract: A composition useful for viscosifying a water-based fluid is provided which comprises a polymer such as guar gum, a metal compound such as an aluminum compound. The composition can also contain a polymer such as guar gum, a magnesium compound such as magnesium oxide, a metal aluminate such as sodium aluminate or a metal compound such as an aluminum compound, and optionally a fatty acid or salts thereof. The water-based fluid can also contain a clay such as bentonite. A process for viscosifying a water-based fluid and for substantially retaining the viscosity of the water-based fluid is also provided which comprises contacting the fluid with the composition described herein. Also disclosed is a process for controlling water loss of a water-based drilling fluid wherein the process comprises contacting the fluid with the composition described herein.