We formulate the concept of minimal fibration in the context of fibrations in the model category SC of C-diagrams of simplicial sets, for a small index category C. When C is an EI-category satisfying some mild finiteness restrictions, we show that every fibration of C-diagrams admits a well-behaved minimal model. As a consequence, we establish a classification theorem for fibrations in SC over a constant diagram, generalizing the classification theorem of Barratt, Gugenheim, and Moore for simplicial fibrations (Barratt et al. in Am J Math 81:639–657, 1959). © 2019, Tbilisi Centre for Mathematical Sciences.