The flow of polymer solutions and gels in porous media, with or without mass transfer, needs to be understood for many applications, including petroleum reservoir engineering, especially drilling and improved hydrocarbon recovery. In the simulation of polymer flow through porous media, it is essential to have good models to describe and to quantify the rheology of polymer solutions and gels in porous media. This paper presents the results of an extensive study aimed at describing and quantifying the viscoelastic properties of polymer solutions and gels for oil and gas recovery operations. Using different water soluble polymers core flood tests and rheological investigations were performed to examine the influence of viscoelasticity on flow behaviour and injectivity of polymer solutions and weak gels in porous media. From the experimental results, it appears that beyond a critical flow rate the viscoelasticity of certain synthetic polymer solutions and gels is reflected by increasing of their in-situ viscosity. The onset of this critical flow rate is influenced by many factors such as molecular weight, hydrolization degree and concentration of polymers as well as core permeability, temperature and salinity. To quantify the viscoelastic effects of polymers in porous media, a modified Maxwell-Fluid-Relation was used. Applying this method, a viscoelasticity index E can be determined, which represents the relaxation time of polymer molecules in porous media. Therefore, it can be used to quantify the viscoelastic flow behaviour of polymer solutions and gels in porous media.