The　design　of　metal　silo　structures　is　dominated　by　the　need　to　resist　shell　buckling　failures　in　service.　Shell　buckling　can　occur　in　many　different　modes,　and　the　strengths　are　very　sensitive　to　the　form　and　amplitude　of　very　minor　deviations　of　geometry　(geometric　imperfections)　from　the　ideal　shape.　Many　imperfection　forms　have　been　studied　in　the　theoretical　literature　on　shell　buckling,　but　only　one　study　appears　to　have　ever　extensively　and　rigorously　measured　the　imperfections　in　real　full-scale　metal　silos:　this　is　the　study　of　the　10,000　tonne　Port　Kembla　grain　silos　in　NSW,　Australia.　The　data　from　this　study　of　three　seemingly　identical　silos　are　very　extensive　and　cannot　be　assimilated　without　considerable　processing.　In　this　paper,　the　first　attempt　is　made　to　provide　a　full　characterisation　of　the　imperfection　set　in　a　manner　that　permits　them　to　be　used　in　shell　buckling　analyses　of　the　silo　shell　that　do　not　rely　on　simplifying　assumptions.　(c)　2005　Elsevier　Ltd.　All　rights　reserved.