Methyl esters of sunflowerseed oil fatty acids can be produced satisfactorily by reaction with the oil in situ. Experiments were designed to determine how variations in molar ratio of methanol to oil, amount of acidic catalyst, and time and temperature of reaction affected the yield and properties of esters. Good results were obtained in mild reaction conditions (temperature 30 degrees C) with a strong acidic catalyst and high molar ratio The fatty ester composition and properties of the products derived from reactions in situ is essentially the same as that from conventional tranesterification of the pre-extracted oil. It is of obvious importance that the products obtained by in situ reaction be as suitable as a diesel fuel substitute as those derived from the conventional treatment.