Pulsed field gradient (PFG) NMR techniques are used to observe restricted diffusion phenomena in systems of fluids in restricted geometries. Model porous media of 8 different size bead packs (closely-packed glassbead of 8 different size ranges) have been engaged to observe the apparent diffusivity using the PFG NMR stimulated echo sequence. Carrying out this type of experiment in the different pore size systems reveals the dependence of the apparent diffusivity on the pore sizes. The diffusion-tine dapendence of the apparent diffusivity is an important parameter for characterizing the non-uniformity of pore structure. Parameter estimation procedure for analyzing NMR diffusion experiment funds multicomponent fashion of apparent diffusivity indicating different distribution of pore size.