In this work, the biodiesel production process using high-phosphorous content raw materials is studied. The objective is to determine the phosphorous mass balances, in order to determine the amount of this element in each stream of an integrated process including esterification, transesterification, and glycerin purification. It was found that up to 97% of the initial phosphorous content in the oil is accumulated in the glycerin phase. The small amount of phosphorous left in the biodiesel phase after decantation is eliminated during the add extraction carried out to purify the biodiesel. The evaporation of methanol after the reaction plays a major role in the quantity of phosphorous and soaps left in the biodiesel phase. For example, with a crude soybean oil containing 226 ppm of phosphorous, the methanol content at the end of the reaction in the biodiesel phase is 4.6 wt.%, being the phosphorous content 7.1 ppm, and the soap concentration 3.89 g/kg. The methanol was evaporated in such a way that its concentration dropped to 0.35 wt.%, and the phosphorous and soaps concentrations decreased to 4 ppm and 0.7 g/kg respectively. This has a direct impact in the quality of the final biodiesel. During the esterification, also an important amount of phosphorous is eliminated from the biodiesel phase. (c) 2010 Elsevier B.V. All rights reserved.