The effect of additives on synthetic barite crystals, prepared under conditions chosen to mimic encountered in off-shore oil fields, has been extensively studied. The addition of certain stereochemically related diphosphonates produces a characteristic morphology change which has been shown to be consistent with a binding model in which the diphosphonate ion replaces two sulfate ions in the (011) surface. A detailed understanding of the recognition processes involved has now led to the rational design of new surface-active molecules with greatly improved efficacy, and a greater appreciation of the factors influencing morphological changes resulting from inhibitor interference.