"Amargasaurus" is classified as a member of the Dicraeosauridae, a family ranked clade within the Diplodocoidea. Currently, this clade consists of nine species belonging to eight genera. These include "Lingwulong shenqi" from the Early or Middle Jurassic of China and four species from the Late Jurassic: "Brachytrachelopan mesai" from Argentina; "Suuwassea emilieae" from the Morrison Formation of the United States; and "Dicraeosaurus hansemanni" and "Dicraeosaurus sattleri" from the Tendaguru beds of Tanzania. "Amargasaurus" was the first dicraeosaurid known from the Cretaceous, although additional dicraeosaurids from the Lower Cretaceous have been described more recently, including "Pilmatueia faundezi", "Amargatitanis macni", and "Bajadasaurus pronuspinax", which are all from Argentina. An unnamed specimen from Brazil indicates that this group persisted at least until the end of the Early Cretaceous. Most analyses find "Dicraeosaurus" and "Brachytrachelopan" to be more closely related to each other than to "Amargasaurus".