2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/95667We start the classification of smooth projective threefolds X whose anticanonical bundles -K_X are big and nef but not ample. In this paper we treat the case b_2(X) = 2 and the morphism associated with the base point free linear system |-mK_X|, m>>0, is divisorial.51 pages, LaTeX2e; final version, to appear in Math. AnnAlgebraic Geometry14J45, 14J30, 14E05text