Lost circulation continues to be a very significant cost in many regions of the world. Many millions of dollars and much rig-time are lost fighting lost circulation and the resulting consequences. The highest costs are to be found when lost circulation occurs in reservoir sections and inappropriate, formation damaging, lost circulation materials are committed to the wellbore causing production impairment. Care must be taken to ensure that any and all LCMs used in reservoir sections do not cause irredeemable damage to producing zones.