An oscillating gradient spin-echo (OGSE) pulse sequence was used to measure the apparent diffusion coefficient (D app ) of water in the short diffusion time regime in the presence of restrictions. The diffusion coefficients of water in a simple water sample and a water and oil mixture were measured to be the same for different periods of the gradient oscillation, as expected when there are no restriction effects. The D app of water in the spaces between closely packed beads was also measured as a function of the gradient oscillation periods in the range 11 to 80 ms. The D app of water in restricted systems varies with the period of the gradient oscillation and the dispersion depends on the scale of the restriction. For a sample of packed beads of diameter 9.1 Ψ 0.7 m, the pore surface-to-volume ratio was estimated experimentally by this method to be 1.3 Ψ 0.1 m Ψ1 , corresponding to a mean pore diameter of 6.4 Ψ 0.7 m. A Monte Carlo computer simulation of the NMR OGSE signal from the spins diffusing in a system of compartments was also implemented and the D app demonstrated similar behavior with gradient oscillation periods.