The present work is concerned with experimental results of rheological characteristics of polyacrylamide (PAM) and of partially hydrolyzed polyacrylamide (HPAM) (degree of hydrolysis up to 80%) in aqueous and aqueous/sodium chloride solutions with changing experimental conditions such as polymer concentration, temperature, solvent quality, and shear rate applied. It has been observed that the all-aqueous and aqueous/NaCl solution of PAM and of HPAM exhibited the non-Newtonian behavior with shear-thinning and shear-thickening areas. The onset of shear-thickening at (gamma) over dot = (gamma) over dot(c) depends mainly on the degree of HPAM hydrolysis, as well as on solution concentration, temperature, solvent quality, and polymer molecular weight. Rheological parameters from power law (Ostwald de Waele model) and activation energy of viscous flow (E-a) are determined and discussed. The changes in apparent shear viscosity during aging of solutions of PAM and HPAM are also described. (c) 2006 Wiley Periodicals, Inc.