Glycerolysis of methyl stearate and tristearin has been carried out in the presence of alkylguanidines-strong nonionic bases-as catalysts. When applied at 10 mol%, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,2,3-tricyclohexylguanidine, and 1,3-dicyclohexyl-2-n-octylguanidine give monoglycerides in more than 90% selectivity, in a maximum of 6 h reaction time.