TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The preparation of the heterogeneous catalyst system further comprises: combining together in a predetermined ratio, a first solution of zinc nitrate, a second solution of lanthanum nitrate, and a third solution of urea, to form a mixed solution; separating and collecting any precipitated solids from the liquid present in the mixed solution; drying the collected solids for a predetermined amount of time; and calcining the solids at 450 degrees C. The preparation of the heterogeneous catalyst system comprises: a mixture of zinc and lanthanum oxides including zinc oxide, lanthanum oxycarbonate (La2CO5), and/or lanthanum oxyhydroxide (LaOOH); and a mixture of zinc and lanthanum oxides including a combination of oxides having the Zn:La bulk molar ratio of 1:0-0:1 or 3.5:1:0, and the surface area of 12.2-16.8 (preferably 15.7) m2/g, the surface composition comprises Zn2+ (4.2-26.8% preferably 26.8%), La3+ (2.1-7.9%, preferably 2.8%), and Olat (19.9-37.5%, preferably 30.5%), the surface atom ratio for Zn2+:La3+ is 1.4:1-11.6:1, preferably 9.6:1, and the surface atom ratio for (Zn2+ + La3+):Olat is 0.2:1-1.1:1, preferably 1.0:1. The step of placing the unrefined oil feedstock in contact with the catalyst system to form a reaction mixture includes an oil with free fatty acid (greater than 4 wt.%) or with water (greater than 3 wt.%). The step of placing the unrefined oil feedstock and an alcohol in contact with the catalyst system to form a reaction mixture includes the alcohol to oil having a molar ratio of greater than 36. Preferred Components: The mixture of lanthanum oxides comprises La2CO5, and/or LaOOH. EXAMPLE - Zinc nitrate (2 M) and lanthanum nitrate (1M) solutions were prepared with distilled water. Then, solutions with varying ratio of zinc:lanthanum (1:0, 1:1, 3:1, 9:1, and 0:1) were mixed with urea (2 M) solution. The mixture was boiled for 4 hours, and then dried at 150 degrees C for 8 hours, followed by step-rising calcination at 250 degrees C, 300 degrees C, 350 degrees C, 400 degrees C, and finally at 450 degrees C for 8 hours. The catalysts were labeled according to their catalyst composition as Zn(10)La(0), Zn(1)La(1), Zn(3)La(1), Zn(9)La(1), or Zn(0)La(10). The catalytic transesterification, esterification, and hydrolysis reactions were conducted in a stainless stirred reactor (500 ml). The transesterification reactions were conducted using oil (126 g), methanol (180 g), and a catalyst (3 g). During the reaction, the reaction mixture (15 ml) was collected via a two-stage liquid sampler at various time intervals, when the reaction was completed, the catalyst and liquid product were separated by filtration. The esterification reactions were performed using oleic acid (126 g), methanol (180 g), and Zn(3)La(1) catalyst (3 g). The liquid product obtained was vaporized to remove any excessive methanol, and then placed into a separating funnel and allowed to settle or separate into layers and separating the upper layer to give a biodiesel.