The hydrogenation of the triglyceride oil, soya bean oil, has been studied in the temperature range 130-160 OC and in the pressure range 100-600 kPa using (i) a 5% w/w Pd/C slurry catalyst and (ii) a 3% w/w Pd/Al2O3 Raschig ring catalyst in a cocurrent downflow contactor (CDC) reactor. Separate studies of residence time distribution (RTD) were carried out in a modified CDC device in order to determine dispersion numbers and dispersion coefficients. The RTD measurements indicated that the overall flow was a mixture of well-mixed and plug flow for the unpacked CDC, so that the entry section (0-30 cm from entrance) was perfectly mixed and the remainder of the column (30-130 cm) gave predominantly plug flow behaviour. The introduction of random packing in the form of 13 mm Raschig rings gave rise to increased back mixing in the lower part of the CDC and the overall dispersion number increased due to liquid and gas circulation around the packing elements. Kinetic studies revealed an initial rate reaction order of 1.24-1.26 with respect to hydrogen concentration both in slurry and fixed bed CDC reactors and is interpreted as a combination of a parallel pair of first and second order reactions during the initial stages of reaction. Mass transfer coefficients for gas absorption (k(L)a) and liquid-solid mass transport (k(s)) were determined for both types of reactor. The k(L)a values lay in the range 1.0-3.33 s(-1) and the liquid-solid transport resistances (X-LS) Were all <1%, so that the reaction was almost totally surface reaction rate controlled. Apparent energy of activation measurements gave values of E-A = 49 +/-6kJ mol(-1), which is strongly indicative of surface reaction rate control involving the hydrogenation of an olefinic double bond. The selectivity in respect of Linolenate (three double bonds) removal and Linoleate (two double bonds) retention was high with, for palladium, relatively low trans-isomer production (<30%). The overall selectivity was slightly, but significantly, better for the fixed bed CDC reactor and this is attributed to the greater degree of plug flow behaviour in the latter, despite the bed causing an increase in dispersion number. However, there is no reaction in the well-mixed section of the fixed bed CDC reactor as there is in the slurry CDC reactor and this is likely to improve selectivity in a consecutive reaction sequence.