Mudflows, faults, surface scarps, and other deformational features, which indicate that the seafloor may be experiencing continuous or intermittent movements, are present on the outer continental shelf and upper slope offshore Louisiana and Texas. Possible mechanisms causing instability and soil movement include hurricane waves, various forms of gravity-driven slope failure, and other geologic phenomena. The magnitude and rate of soil movements and the forces these movements transmit to structures must be estimated for design of offshore production facilities. Lateral forces on offshore structures due to soil movement can exceed 20 million Newtons (20,000 kN). A quantitative analysis of soil deformation and structural loading requires a comprehensive interdisciplinary stu y of the geologic and oceanographic environment. Analytic procedures to evaluate the stability of a site include finite-element analyses and limit-equilibrium methods. Data for these analyses should be based on well-planned geophysical and geotechnical site investigations and engineering laboratory testing.