Acid oils represent a low-cost feedstock for biodiesel synthesis. The aim of this work was to study a single-step enzymatic esterification and transesterification process for fatty acid ethyl esters (FAEEs) production employing acid oils, ethanol, and liquid lipase formulation. The effects of lipase source (CALB, Palatase 20000?L, Lipolase 100?L, and Callera Trans L), temperature and enzyme ratio were studied in the transesterification of refined soybean oil with ethanol. The highest yield esters content (97%) was obtained at 30??C with 10% vol/vol of Lipolase 100?L. The ethanolysis of acid soybean oil, using soybean oils with different acid contents (acid value (AV): 8.5, 50, and 90), was investigated using 10% vol/vol of lipase at 30??C. The highest esters content (71%) was obtained employing acid oil with AV 50 and Palatase 20,000?L. The results showed the significant performance of soluble lipases in transesterification reactions of acid oils aiming for FAEEs synthesis.