hydrogenation of sunflower oil to oleomargarine (70 iodine index) was studied from data obtained using a central composite experimental design. The nickel on silica catalyst was made by precipitation-deposition. The reaction was performed in a semi-batch reactor at temperatures between 120 degrees C and 180 degrees C, hydrogen pressures from 2.5 to 4.5 bar and catalysts loadings of 0.012-0.039% (Ni/oil). Response surface methodology was used to predict the effect of reaction temperature, hydrogen pressure and catalyst loading on the overall rate constant of hydrogenation, total trans-isomers and stearic acid triglycerides production. Statistical assessment showed a good agreement between predicted and observed values. (C) 2008 Elsevier Ltd. All rights reserved.