Vegetable oils and animal oils have been used as quenchants for metals for thousands of years; however, it hasn’t been until relatively recently that their cooling properties have been studied in a thorough, quantitative manner. This review will focus on the published data relating to the use of triglycerides from various animal and vegetable sources to quench-harden steels. Particular focus will be on the traditional selection and use of different vegetable and animal oils for steel hardening applications and the cooling time-temperature behavior of these fluids to characterize their quenching performance. This information has not been previously reviewed in this manner.