The application of vegetable oil as an insulating fluid is gaining a lot of interest from researchers all over the world because of the fact that it is a renewable source and is easily available. This paper reviews and compares the preparation methods of vegetable oil-based nanofluids that have been used by many different authors. The experimental results obtained by previous researchers on the insulating properties of the vegetable oil-based nanofluids are also analysed and discussed in detail. In addition, future improvements for experimental works with insulating nanofluids are also proposed.