This study was aimed at the association and effective hydrodynamic thickness of hydrophobically associating polyacrylamide (HAPAM) through porous media with coreflow experiment. It shows that there is strong hydrophobic association for HAPAM in porous media but not for polyacrylamide (PAM). The resistance factor and effective hydrodynamic thickness of HAPAM are obviously superior to those of PAM. HAPAM exhibits much stronger shear thinning behavior than PAM due to the ability to form transitional network structure. It also indicates that PAM can exhibit a transition from shear thinning behavior to shear thickening behavior at low polymer concentration. (C) 2008 Wiley Periodicals, Inc.