The researchers investigated using acid oil, a byproduct of the vegetable oil industry, as a source of biodiesel. They developed a new esterification process to produce biodiesel from acid oil and compared its fuel properties with standard biodiesel and diesel fuel. Blends of biodiesel and diesel fuel were also prepared and tested. The study found that biodiesel produced from acid oil can be a viable alternative fuel source, with comparable properties to standard biodiesel and diesel fuel.