In this work, the porous media flow of polymer solutions of poly(ethylene oxide) (PEO), hydrolyzed polyacrylamide (HPAA), and their blends is investigated. Aqueous solutions of PEO exhibit critical extension thickening when flowing through porous media. HPAA solutions also exhibit critical extension thickening in excess salt environments, but their behavior changes to a more gradual extension thickening when dissolved in deionized water. The mixtures of solutions of HPAA and PEO therefore vary its porous media flow behavior, depending on the ionic environment. In deionized water, a critical extension thickening similar to that obtained with PEO is still observed when HPAA is mixed in at concentrations low enough so that its apparent viscosity does not mask the influence of PEG. In the presence of salt, only a critical extension thickening is observed, which is attributed to transient network formation of both PEO and HPAA molecules. The mixtures generally exhibit a less critical behavior and display a lower than expected sensitivity of the onset Reynolds number for extension thickening with concentration. The results presented herein indicate that interspecies molecular interactions through transient network formation and the associated flow modification play a major role in determining the complex non-Newtonian flow behavior of these polymer solutions.