The transesterification of rapeseed oil with methanol has been studied in the presence of eight substituted cyclic and acyclic guanidines and compared with unsubstituted guanidine. The catalytic activity of the guanidines depends mainly on their intrinsic base strength. With a long alkyl chain on the guanidine, no lipophilic effect is observed. The best catalyst found is commercial 1,5,7-triazabicyclo[4.4.0] dec-5-ene which, when used at 1 mol%, produces a 90% yield of methyl esters with 1 h of reaction time.9926570