The rheology of concentrated and bulk polymer systems has been investigated. Studies have been made on a low molecular weight series of several polymers using capillaries and a high shear concentric cylinder viscometer. The compositional and shear conditions for non‐Newtonian flow have been closely defined. Limiting high and low shear viscosities and the path of non‐Newtonian flow may be consistently correlated for concentrated systems of linear, flexible polymers. The minimum molecular weight for non‐Newtonian flow is related to the transition at low shear in log viscosity vs log molecular weight correlations. For non‐Newtonian systems, changes in apparent activation heat for viscous flow are reported as a function of shear. The conditions for laminar flow shear degradation of polymers are also given.