Spherical shells are extensively used as structural elements. As they are subjected to different loading conditions, compressive membrane forces develop causing failure due to compressive stability. In order that the shells perform their design function adequately, sufficient design margins should exist. These design margins are established by means of experimental tests and numerical analysis. Comparisons between classical, theoretical and experimental results for spherical shells subjected to external pressure loading demonstrated large discrepancies. These discrepancies are attributable to material and geometric imperfections resulting from fabrication methods.;Sufficient design information with respect to the imperfections is required to perform numerical analyses. The present study addresses these concerns with regard to three commonly occurring loading types, viz., external pressure, gradient loading and a ring loaded axisymmetric penetration.;The material imperfections were modeled by a stress strain curve derived from test results or by a cold bending simulation. For each of the loading cases, the perfect shell behavior was initially investigated. The worse axisymmetric imperfection was determined by examining the buckling loads due to various imperfection shapes using the derived stress strain curve. Sensitivity studies using the identified critical imperfection were performed over a range of shell radius to thickness ratios. The results were compared with the available experimental results in case of external pressure loading.;Based on the numerical analysis, appropriate design recommendations in the form of a worst imperfection were made for each of the loading cases. In addition, graphical design aids relating imperfection amplitudes and the ASME Boiler and Pressure Vessel Code recommended tolerances were presented for external pressure loading. The imperfection amplitudes with regard to other type of loadings were to be governed by the tolerances. It was also demonstrated that the derived stress strain curve can be used adequately to model the material imperfections by comparing the resulting buckling loads with those predicted by the cold bending simulation.