This paper reviews the production and characterization of biodiesel fuel from vegetables oils as well as the experimental work carried out via supercritical ethanol transesterification. Biodiesel, which can be used as an alternative diesel fuel, is made from renewable biological sources such as vegetable oil and animal fats. More than 100 years ago, a brilliant inventor named Rudolph Diesel designed the original diesel engine to run on vegetable oil. There are moe than 350 oil-bearing crops identified, among which only sunflower, safflower, soybean, cottonseed, rapeseed, and peanut oils are considered as potential alternative fuels for diesel engines. The major problem associated with the use of pure vegetable oils as fuels for diesel engines are caused by high fuel viscosity in compression ignition. Dilution, micro-emulsification, pyrolysis, and transesterification are the four techniques applied to solvge the problems encountered with the high fuel viscosity. Dilution of oils with solvents and microemulsions of vegetable oils lowere the viscosity, and some engine performance problems still exist. The purpose of the transesterification process is to lower the viscosity of the oil. The transesterification of triglycerides by methanol, ethanol, propanol, and butanol has proved to be the most promising process.