The ultimate capacity of offshore platform conductor strings is studied. The unique way in which conductors are loaded is described and the various design methods that exist are presented. Previous research in the field of tubular member behavior is also reviewed. The results of seven experimental tests are evaluated and compared with the existing conductor design criteria. The test matrix calls for various amounts of lateral loading to be imposed on the conductor system. Axial load, applied to simulate the weight of inner casings, is then applied until failure. Results indicate that internally applied axial loads do not induce stability related failure in the outer conductor. Additionally, the design internal moment, which is based on an inner casing being as eccentric as possible, accurately represents the upper limit for the bending moment observed in the experimental tests. The flexural stiffness of the inner casing serves to strengthen the conductor system. Therefore, a design method that considers the strength of the outer conductor and the inner casings is recommended. / Master of Science