Lost circulation materials are used to prevent fluid losses into the formation. Spacer or cement fluids can be lost into the formation through seepage losses, natural or induced fractures, or vugs. The larger the opening into the formation, the more serious the risk of losses, and the more aggressive the lost circulation solution will need to be. If lost circulation is severe (significant to total losses), the losses will need to be cured before starting a primary cementing operation, typically with a lost circulation material “pill” or a cement plug treatment. If losses are milder, lost circulation materials can be added to spacers and slurries to reduce the losses to the formation as the fluids are being pumped. Lost circulation materials tend to fall in three categories: fibers, flakes, and granules. These can be pumped individually or in various combinations, and in stand-alone fluids, spacers, or cements.