Hazard and Operability studies are now being used by a variety of industries to reveal potential weaknesses in new and existing plants. The method pioneered by ICI has been adapted by various Hazop study leaders to suit the needs of other companies, using strategies differing somewhat from the CIA Guide. These changes are illustrated by the results of Hazop studies led by the author for clients in the chemical, offshore and water industries. The paper presents techniques for maximizing the effectiveness of Hazop studies.