Equations widely used for casing design ignore the effects of the cement sheath on collapse resistance and assume uniform collapse loading of the casing. The study presented in the full-length paper describes the effects on collapse loading conditions of the mechanical properties of cement and the formation surrounding the casing string. The finite-element-analysis (FEA) technique was used to investigate these effects. According to the results of this study, improvements of as much as 62% in casing collapse resistance can be achieved, depending on the mechanical properties of the cement systems and formation properties.