The condensation of technical-grade oleic acid (OA) (65%, 85%, and 90% oleic acid) with glycidol (Gly) was carried out in an aqueous medium in the presence of a macroporous anion-exchange resin containing ammonium groups. The reaction was optimized by a unifactorial method and by a 2(n-1) fractional factorial plan. The effects of the following main parameters were quantified from experiments based on a 2((5-1)) = 2(4) factorial design: OA/Gly molar ratio, concentration (mmol of OA/mL of H2O), catalytic efficiency (mequiv of X/mmol of OA), and temperature. The conditions were optimized for a discontinuous process in a stirred reactor for selective synthesis of glycerol 1-monooleate (1-GMO) in a polymorphic system (solid resin/emulsion or microemulsion) consisting of OA/Gly/H2O/1-GMO. The catalytic role of the Ambersep 900-X resin was demonstrated by conducting the reaction using the resin in the different functional forms Ambersep 900-OH- and Ambersep 900-HCO3- and in the nonfunctionalized form Ambersep 900-Cl-. The highest yield of 1-GMO (97%) was obtained with the nonfunctionalized form Ambersep 900-Cl- at 70 degrees C.