Iodine value and the yield of trans isomers on hydrogenation of soybean oil using nickel supported on silica/alumina catalyst were measured. The empirical model was established to study the effect of temperature, pressure, the concentration of catalyst, and the speed of agitation, on reaction rate. Oils with varying concentrations of sulfur, phosphorus, chlorine, and nitrogen compounds have been hydrogenated over the nickel-based catalyst to study the effect on rate and trans-isomer formation. A comparison was made to study the effect of these four catalyst poisons on hydrogenation catalysts using the relative hydrogenation efficiency.