The viscoelastic behavior of commerical and model hydrophobically modified, ethoxylated urethane (HEUR) polymers is examined in aqueous solutions, alone and in the presence of sodium dodecylsulfate (SDS). An unmodified poly(oxyethylene) and a linear model HEUR thickener without internal hydrophobes are compared with three commercial HEUR thickeners, one of low molecular weight comparable with the model HEUR and two of higher molecular weight, comparable to the unmodified poly(oxyethylene). Shear thickening in the viscosity‐shear rate profile, storage and loss moduli, die swell, and dynamic uniaxial extensional viscosity behaviors are examined. There is general agreement among the elastic functions for the low molecular weight commercial HEUR which is primarily inelastic and for one of the higher molecular weight commercial HEUR thickeners, which exhibits a strongly elastic behavior. The addition of SDS to aqueous HEUR solutions increases solutionviscosity; in one of the high MW HEUR thickeners this increase is associated with an increase in the elasticity of the solution. In the lower molecular weight HEUR, the increases in solutionviscosity observed with SDS are not associated with a notable change in the elasticity of the solution. The difference in rheological response is interpreted not in terms of ‘‘real’’ molecular weight differences, but in terms of competition between intra‐ and interhydrophobe associations. Other differences are discussed and compared with the rheological response of a low molecular weight model HEUR thickener without internal hydrophobic linkages.