Prediction of the thermal capability of a fast breeder spent fuel shipping cask requires consideration of a large number of variables, such as geometry, canister packing fluid, gaseous coolant pressure, surface emissivities, and fin densities. In order to evaluate the individual influences of the large number of controlling parameters, a parametric analysis of a conceptual cask has been performed. Results of the analysis are applied to four options, each having a different configuration. Comparison of the options indicates that substantial increases in cask thermal capability may be obtained by the use of liquid sodium as a primary coolant and aluminum as a basket material.