Experiments on spontaneous imbibition processes in Hele-Shaw cells were carried out in squared cells (20 cm × 20 cm) with separations of 0.005, 0.015 and 0.075 cm using twice-distilled water and Soltrol 170 as the displacing and displaced fluids, respectively. The experiments indicated that it was possible to repeat the main features of the spontaneous imbibition process using a procedure for wettability restoration of the glass sheets. The best sweep efficiency was achieved for the 0.015 cm cell gap. Two or three consecutive stages occurred depended on the cell gap, as evidenced by a characteristic speed and a characteristic advancing front structure. The initial stage speed/development stage speed ratio and the oil total area/water-oil total interfacial length ratio as functions of time were gap-dependent. The capillary number and interfacial power density estimations indicated that at about 0.033 cm gap there was a flow pattern transition from slightly uniform displacement to fingering flow.