Alkalinity Control in most invert emulsion mud is obtained by the addition of common calcium hydroxide or in calcium oxide. The use of a calcium base is particularly relevant when tall oil fatty acid soaps are in use. Oil-base muds do not suffer from the problems of hydrogen sulfide or carbon dioxide contamination that can occur in a water base fluid. However, such contamination in an oil base mud will show itself as the increased addition rate of lime to maintain alkalinity.