Vegetable oils have become more attractive recently because of their environmental benefits and the fact that it is made from renewable resources. Vegetable oils do not contain any sulfur, aromatic hydrocarbons, metals, or crude oil residues. Short-term engine tests indicate good potential for vegetable oil fuels. Long-term endurance tests may show serious problems in injector coking, ring sticking, gum formation, and thickening of the lubricating oil. The high viscosity of vegetable oil reduces fuel atomization and increases fuel spray penetration. The vegetable oils, as alternative engine fuels, are all extremely viscous with viscosities ranging from 10 to 20 times greater than that of petroleum diesel fuel. Modern diesel engines have fuel-injection systems that are sensitive to viscosity changes. A way to avoid these problems is to reduce the viscosity of vegetable oil in order to improve its performance. There are some methods to reduce the viscosity of vegetable oil. The purpose of this work is to investigate potential solutions for solving the problem of vegetable oil viscosity.