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The increasing development of materials technology and the consequent rise in complexity of structures, demand a proper knowledge of the safety levels involved in the design. The reliability techniques applied to structural analysis allow dealing with the uncertainties inherent in the design of structures, so that the failure probability can be predicted since the design stage. In this context, the design variables are described as random variables, within the choice of an adequate distribution model to represent data is required. In an oil and gas well scenario, the casing design is a crucial stage of the whole project, representing the major structural elements responsible to maintain the well integrity through its lifetime, allowing adequate production activities. The occurrence of failures in casing systems can lead to irreversible safety problems in well operation. For the evaluation of the strength of the tubes used in casing design, the code API 5C3: 1994 is widely applied by several companies overall. This deterministic formulation cannot deal with the uncertainties associated with the tube manufacturing process, as variations in geometrical and mechanical properties. This paper addresses the analysis of casing strength in a reliability-based approach, regarding the failure modes usually verified in well casing design. The reliability analysis is performed by the Monte Carlo simulation and the First/Second Order transformation methods (FORM/SORM). The safety levels associated to the referred formulation are estimated and discussed.