Hot Lime and quick lime are all common names for calcium oxide (CaO). It reacts with water to form calcium hydroxide (lime, Ca(OH)2). Hot Lime can supply calcium ion in calcium treated drilling fluids that can control the hydration and dispersion ability of clay and keep it in the state of moderate flocculation. Moreover, Hot Lime can be used as a source of calcium and alkalinity in oil-base muds. In wet or rainy environments, calcium hydroxide should be used instead of hot lime. In conventional oil mud systems, hot lime will react with the emulsifiers to form calcium soaps. Hot Lime reacts with water to evolve heat, the evolution of heat may be helpful in building emulsions. Hot Lime can be used in oil-base mud systems as a source of alkalinity when drilling acid gases, such as carbon dioxide and hydrogen sulfide.