Lime is used as a source of calcium and alkalinity in both water- and oil-based drilling fluids. Lime, a widely available commercial chemical, is an economical source of calcium (Ca2+) and hydroxyl ions (OH–).

Drilling fluid applications for lime include increasing pH, providing excess lime as an alkalinity buffer, flocculating bentonite muds, removing soluble carbonate (CO32–) ions, controlling corrosion, and activating fatty-acid, oil-based mud additives.