Embodiments relate to methods for assessing inaccessible pore volume for polymer flooding. The methods include utilizing nuclear magnetic resonance to monitor polymer-based fluid displacements into porous media. According to an embodiment, the method includes providing a core sample of a porous medium, determining a total pore volume of the core sample, introducing polymer solutions, obtaining nuclear magnetic resonance relaxation time distributions of water within the core sample, and assessing the inaccessible pore volume.