Two natural smectites, Na+- and Ca2+-montmorillonites, were contacted with NaCl solutions at concentrations between 0.05 and 0.70 mol/L; further, KCl as a swelling inhibitor and an alkylamido betaine and alpha-olefin sulfonate mixture used as a foaming surfactant for the water alternating gas (WAG) process were added separately to the saline solutions. The mean crystalline swelling and the distribution of the particle thickness arranged as a pile of sheets and oriented perpendicular to the 001 diffraction direction were calculated from the X-ray diffractograms and according to literature methods; the mean crystalline swelling was tested against Monte Carlo molecular simulation results from our previous works. Distribution of the clay particle thickness indicates the fuzziness of the transition between the crystalline and osmotic swelling; this method clearly shows the presence of osmotic swelling not detected on the basis of the other methods. The degree of osmotic swelling depends upon the nature of clay; it is more evident for Ca2+-montmorillonite, especially in the presence of KCl and the selected surfactant. The results are oriented to improve the selection of water salinity and type of surfactant for the WAG recovery process.