Well casing represents a significant portion of total well cost. The full-length paper presents a study of multistring-casing-design optimization that considers complex load conditions, annular-fluid expansion, and wellhead growth. Casing strings for different drilling phases are selected to reduce tabular cost without sacrificing safety and well integrity. An interval branch-and-bound optimization technique is used to find global minima of the cost function. A new concept of wellhead-growth index (WGI) is introduced.