Initial postbuckling analysis provides a well-established framework to assess the imperfection sensitivity of shell structures. A finite element implementation of the approach makes it possible to analyse the nonlinear buckling behaviour of practical and large shell structures. For structures with complicated nonlinear behavior in which modal interactions are important, such as cylindrical shells, a multi-mode analysis is required. In the present work, coupled mode analyses are carried out and b-factors and limit-point loads of imperfect structures are calculated. Steps towards the development of selection criteria for the modes to be included in the imperfection sensitivity analysis are illustrated.