There is a need for the growing generation to find new and alternate energy sources instead of conventional depleting energy resources. The increasing environmental pollution due to conventional fuels has taken interest to search for new alternative sources that are environmental friendly and can replace the conventional fuels such as biodiesel. The biodiesel can best and efficiently produced using waste cooking oils. Waste cooking oils generally we get from restaurants are commonly just thrown away. Those oils do not have any treatment first, and it pollutes the environment. One of the ways to treat the waste oil is by converting it to biodiesel. The main aim of this review is to show the comparative study of production of biodiesel by the transesterification reaction of waste cooking oil and various modern refining processes to refine the biodiesel. The biodiesel is obtained by reacting waste cooking oil along with alcohol in the presence of NaOH or KOH as base catalyst.