The State and Federal lands offshore from the modern Mississippi River delta are highly productive of hydrocarbons, and there presently exist a large number of bottom-supported drilling and production platforms in water depths ranging from a few metres to several hundred metres. In addition, thousands of kilometres of pipelines connect these producing wells and production platforms to land-based processing and trunkline facilities. Since exploration began in this area, several large platforms and many pipeline breaks have resulted from subaqueous sediment landslides. The major types of instabilities present have been mapped with a variety of seismic techniques. These maps, used in association with geotechnical tests, have permitted a comprehensive assessment of the mechan sms responsible for formation of the instabilities. The major types present are collapse depressions, bottleneck slides, and elongate mudslides and debris flows. The mechanisms responsible for the formation of these features are rapid sediment loading, buildup of excess pore pressures, cyclic wave loading, and localized oversteepening of the

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bottom. Structures and pipelines emplaced near or within a subaqueous landslide can experience loss of support, lateral displacement, or burial, depending upon the type and location of the landslide.