The effects of some process conditions on the overall reaction rate and on trans isomer formation during hydrogenation of low erucic acid rapeseed oil with a commercial nickel catalyst were studied. Experimental data were correlated by an empirical equation which would be used to predict the reaction rate constants for any given process conditions. Temperature had a major effect on rate and trans isomer formation. Pressure and catalyst concentration, howeve& had only minor effects. It is suggested that apart from these factors, the extent of trans isomer formed is also controlled by the nature and amount of the unsaturation in the oil and by the overall reaction rate. Anew parameter, specific isomerization index was introduced to represent the formation of trans isomers during the hydrogenation reaction.The effects ofsolvents n-hexane and 2-propanol on the reaction rate and trans isomers formation were determined. A c k n o w l e d g m e n t s Financial support was provided by the Natural Sciences and Engineering Research Council of Canada and the Ontario Ministry of Agriculture and Food. Financial support through a NRC postdoctorate fellowship was provided one of the authors (I! S. Atri).