Oligosaccharides consist of more than one monomer. Four-sugar oligosaccharides have four same or different monomers. In this case, two four-sugar oligosaccharides consist of two glucose and two galactose monomers. Still, they are not identical. The sequence of monomers in each oligosaccharide may differ. Also, geometry and location of glycosidic linkages may vary. This two factors, separately or working together, affect the structure of oligosaccharides.