Some surface-active chemicals are able to improve the spontaneous imbibition of water into oil-wet carbonates. In this work, the oil recovery from oil-wet reservoir cores was compared using aqueous solutions of an ethoxylated alcohol (EA) and a cationic surfactant (C12TAB). The experiments were conducted at room temperature using short (similar to5 cm) and long (similar to30 cm) cores with initial water saturation in the range of 17-33%. Due to wide variation in porous structure, the cores were characterized into two groups, i.e., moldic and sucrosic. The former cores had more than 25% of the pore volume (PV) related to vugs, and the latter appeared more homogeneous. The permeability of the moldic and sucrosic cores varied between 20 and 180 and 80-350 mD, respectively. In general, the efficiency of C12TAB was superior to EA regarding spontaneous oil expulsion from the cores. For the short core experiments, about 40-45% of original oil in place (OOIP) was recovered using C12TAB, while only 10% was the average recovery using EA. The available data for the short cores gave no reasons to discriminate between moldic and sucrosic cores regarding oil expulsion. The long 162 mD sucrosic core expelled 65% of OOIP in the presence of C12TAB. The high oil recovery, compared to the short cores, was related to greater impact of gravity forces. The imbibition of EA solution into the long 45 mD core was very small, less than 5%, but large improvements were achieved when changing to C12TAB solution. Contact angle measurements on oil-wet calcite crystals confirmed that C12TAB was much more effective than EA in altering wettability toward more water-wet conditions.