The fact that most fluids in nature do no obey Navier-Stokes eqs. manifests engineering & industrial importance of non-Newtonian fluids. The 2nd and 3rd grade fluids which form a subclass of differential type fluids can predict shear thinning and thickening properties but lack other feathers such as stress relaxation and retardation. Maxwell and Oldroyd-B fluids models which are viscoelastic rate type fluids can show relaxation and retardation phenomena. Burgers fluid which is a viscoelastic fluid model includes an Oldroyd-B, Maxwell and Newtonian fluid models as special cases....