Polysaccharides and Oligosaccharides are both parts of carbohydrate molecules, but they vary in complexity and size. The Oligosaccharides are much easier and smaller, according to the Medical Biochemistry Page. Overall carbohydrates consist of hydrogen, oxygen and carbon. The least are known as monosaccharides that are sugars having just a few carbons, although the largest are called as polysaccharides.